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1.  Triple-Hop Distance as a Valid Predictor of Lower Limb Strength and Power 
Journal of Athletic Training  2008;43(2):144-151.
Context:
Hop tests are functional tests that reportedly require strength, power, and postural stability to perform. The extent to which a triple-hop distance (THD) test measures each of these characteristics is relatively unknown.
Objective:
To determine the extent to which the THD predicts performance on clinical measures of power, strength, and balance in athletic individuals.
Design:
Within-subjects correlational study.
Setting:
Station-based, preseason screening of athletes.
Patients or Other Participants:
Forty National Collegiate Athletic Association Division I-AA men's and women's soccer student-athletes (20 women, 20 men; age  =  20.0 ± 1.4 years, height  =  172.8 ± 9.2 cm, mass  =  71.9 ± 8.9 kg).
Intervention(s):
As part of a comprehensive preseason screening of athletes, participants completed the Balance Error Scoring System (BESS) test, 3 trials each of the THD and vertical jump, and 5 repetitions each of concentric isokinetic quadriceps and hamstrings strength testing at 60°/s and 180°/s. Bivariate correlations and linear regression analyses determined the extent to which THD (cm) predicted each of the strength, power, and balance measures.
Main Outcome Measure(s):
Maximal vertical jump height (cm), total BESS error scores, and quadriceps (Quad60, Quad180) and hamstrings (Ham60, Ham180) isokinetic maximum peak torque (Nm) at 60°/s and 180°/s, respectively.
Results:
Triple-hop distance was a strong predictor of vertical jump height, explaining 69.5% of the variance (P < .01). THD also predicted 56.7% of the variance in Ham60 (P < .01), 55.5% of the variance in Ham180 (P < .01), 49.0% of the variance in Quad60 (P < .01), and 58.8% of the variance in Quad180 (P < .01). No relationships between THD and BESS scores were noted.
Conclusions:
Triple-hop distance is a useful clinical test to predict an athlete's lower extremity strength and power. Although THD was not a predictor of static balance, further research is needed to examine its relationship with more dynamic balance tests.
PMCID: PMC2267326  PMID: 18345338
functional performance tests; peak torque; balance; postural stability; open kinetic chain exercises
2.  Quadriceps and Hamstrings Muscle Dysfunction after Total Knee Arthroplasty 
Background/rationale
Although TKA reliably reduces pain from knee osteoarthritis, full recovery of muscle strength and physical function to normal levels is rare. We presumed that a better understanding of acute changes in hamstrings and quadriceps muscle performance would allow us to enhance early rehabilitation after TKA and improve long-term function.
Questions/purposes
The purposes of this study were to (1) evaluate postoperative quadriceps and hamstrings muscle strength loss after TKA and subsequent recovery using the nonoperative legs and healthy control legs for comparison, and (2) measure hamstrings coactivation before and after TKA during a maximal isometric quadriceps muscle contraction and compare with nonoperative and healthy control legs.
Methods
We prospectively followed 30 patients undergoing TKA at 2 weeks preoperatively and 1, 3, and 6 months postoperatively and compared patient outcomes with a cross-sectional cohort of 15 healthy older adults. Bilateral, isometric strength of the quadriceps and hamstrings was assessed along with EMG measures of hamstrings coactivation during a maximal isometric quadriceps contraction.
Results
There were no differences in strength loss or recovery between the quadriceps and hamstrings muscles of the operative leg throughout the followup, although differences existed when compared with nonoperative and healthy control legs. Hamstrings muscle coactivation in the operative leg during a maximal quadriceps effort was elevated at 1 month (144.5%) compared to the nonoperative leg.
Conclusions
Although quadriceps dysfunction after TKA typically is recognized and addressed in postoperative therapy protocols, hamstrings dysfunction also is present and should be addressed.
Clinical Relevance
Quadriceps and hamstrings muscle strengthening should be the focus of future rehabilitation programs to optimize muscle function and long-term outcomes.
doi:10.1007/s11999-009-1219-6
PMCID: PMC2919870  PMID: 20087703
3.  Influence of Hip-Flexion Angle on Hamstrings Isokinetic Activity in Sprinters 
Journal of Athletic Training  2012;47(4):390-395.
Context
Hamstrings strains are common and debilitating injuries in many sports. Most hamstrings exercises are performed at an inadequately low hip-flexion angle because this angle surpasses 70° at the end of the sprinting leg's swing phase, when most injuries occur.
Objective
To evaluate the influence of various hip-flexion angles on peak torques of knee flexors in isometric, concentric, and eccentric contractions and on the hamstrings-to-quadriceps ratio.
Design
Descriptive laboratory study.
Setting
Research laboratory.
Patients and Other Participants
Ten national-level sprinters (5 men, 5 women; age = 21.2 ± 3.6 years, height = 175 ± 6 cm, mass = 63.8 ± 9.9 kg).
Intervention(s)
For each hip position (0°, 30°, 60°, and 90° of flexion), participants used the right leg to perform (1) 5 seconds of maximal isometric hamstrings contraction at 45° of knee flexion, (2) 5 maximal concentric knee flexion-extensions at 60° per second, (3) 5 maximal eccentric knee flexion-extensions at 60° per second, and (4) 5 maximal eccentric knee flexion-extensions at 150° per second.
Main Outcome Measure(s)
Hamstrings and quadriceps peak torque, hamstrings-to-quadriceps ratio, lateral and medial hamstrings root mean square.
Results
We found no difference in quadriceps peak torque for any condition across all hip-flexion angles, whereas hamstrings peak torque was lower at 0° of hip flexion than at any other angle (P < .001) and greater at 90° of hip flexion than at 30° and 60° (P < .05), especially in eccentric conditions. As hip flexion increased, the hamstrings-to-quadriceps ratio increased. No difference in lateral or medial hamstrings root mean square was found for any condition across all hip-flexion angles (P > .05).
Conclusions
Hip-flexion angle influenced hamstrings peak torque in all muscular contraction types; as hip flexion increased, hamstrings peak torque increased. Researchers should investigate further whether an eccentric resistance training program at sprint-specific hip-flexion angles (70° to 80°) could help prevent hamstrings injuries in sprinters. Moreover, hamstrings-to-quadriceps ratio assessment should be standardized at 80° of hip flexion.
PMCID: PMC3396298  PMID: 22889654
injury prevention; eccentric exercises; length-tension relationship; hamstrings-to-quadriceps ratio; muscle strains
4.  The Influence of Vibration on Muscle Activation and Rate of Force Development during Maximal Isometric Contractions 
At present there appears to be a need for research conducted on the effects of vibration on the contractile ability of skeletal muscle tissue. The aim of this study was to address this issue by examining the effects of a superimposed muscle/tendon vibration at 50.42±1.16 Hz (acceleration 13.24 ± 0.18ms-2: displacement ≈5mm) on muscular activation and maximal isometric contraction. Sixteen participants with a mean age, body mass, and height of 22 ± 4.4 years, 73.2 ± 11.7 kg and 173.1 ± 9.7 cms, respectively, were recruited for this study. Electromyography and accelerometry from the rectus femoris, and maximal isometric force data characteristics were collected from the dominant limb under conditions of vibration, and no-vibration. A superimposed 50 Hz vibration was used during the contraction phase for the maximal isometric leg extension for the condition of vibration. A one-way ANOVA revealed no significant (p > 0.05) differences between the vibration and no-vibration conditions for peak normalized EMGRMS (84.74% Vs 88.1%) values. An ANOVA revealed significant (p > 0.05) differences between the peak fundamental frequencies of the FFT between the conditions vibration (27.1 ± 12.2 Hz) and no-vibration (9.8 ± 3.5 Hz). Peak isometric force, peak rate of force development, rate of force development at times 0.05, 0.01, 0.1, 0.5 seconds, and rate of force development at 50, 75, and 90% of peak force were not significantly different. The results of this study suggest that the application of vibration stimulation at 50 Hz during the contraction does not contribute to muscle activation, or enhance force production for maximal isometric contractions.
Key PointsThe application of a vibratory stimulation to the human body increases the normal acceleration resulting in an increase in force and a change in performanceThis study was to address this issue by examining the effects of a direct superimposed muscle/tendon vibration at 50 Hz on isometric strength characteristicsNo improvement or change in isometric force or rate of force developmentNo changes to peak normalized EMGRMS values
PMCID: PMC3896109  PMID: 24497816
Strength; oscillations; isometric; peak; muscle activation
5.  Variations in Neuromuscular Activity of Thigh Muscles During Whole-Body Vibration in Consideration of Different Biomechanical Variables 
The intention of this study was to systematically analyze the impact of biomechanical variables in terms of different vibration frequencies, amplitudes and knee angles on quadriceps femoris and hamstring activity during exposure to whole-body vibration (WBV). 51 healthy men and women (age 55 ± 8 years) voluntary participated in the study and were randomly allocated to five different vibration-frequency groups. Each subject performed 9 static squat positions (3 amplitudes x 3 knee angles) on a side alternating vibration platform. Surface electromyography (EMG) was used to record the neuromuscular activity of the quadriceps femoris and hamstring muscles. Maximal voluntary contractions (MVCs) were performed prior to the measurements to normalize the EMG signals. A three-way mixed ANOVA was performed to analyze the different effects of the biomechanical variables on muscle activity. Depending on the biomechanical variables, EMG muscle activity ranged between 18.2 and 74.1 % MVC in the quadriceps femoris and between 5.2 and 27. 3 % MVC in the hamstrings during WBV. The highest levels of muscle activation were found at high frequencies and large amplitudes. Especially in the quadriceps femoris muscle, a WBV frequency of 30 Hz led to a significant increase in muscle activity compared to the other tested frequencies. However, it seems that knee angle is only relevant for the quadriceps femoris muscle. The results of this study should give more information for developing individual training protocols for WBV treatment in different practical applications.
Key PointsWBV leads to a higher muscle activity of the quadriceps femoris than of the hamstrings.The maximum levels of muscle activity were significantly reached at high amplitude and high frequency.The knee angle only significantly affects the quadriceps femoris.Certain combinations of the biomechanical variables have similar effects on the level of muscle activity.
PMCID: PMC3772586  PMID: 24149149
Vibration training; surface electromyography; muscle strength; muscle tuning
6.  Joint position sense and rehabilitation in the anterior cruciate ligament deficient knee. 
BACKGROUND: Impaired joint position sense (JPS) has been shown in anterior cruciate ligament (ACL) deficient and osteoarthritic knees. The relation between JPS and function is uncertain. The aim of this study was to determine further if ACL deficient knees show abnormal JPS and the effect of exercise therapy on JPS, and also to assess the relation between JPS, functional stability, and strength. METHODS: Fifty patients (46 men and four women, mean age 26.3 years) with unilateral ACL deficient knees were assessed on admission and after rehabilitation (5 hours a day for four weeks). JPS was assessed by reproduction of passive positioning using a visual analogue incorporating a goniometer. Knee stability was analysed by self report questionnaire (score 0-280) and functional activity test (single leg hop and figure of eight run). Isokinetic dynamometry was performed to evaluate quadriceps and hamstring peak torque strength. Controls were either age and sex matched individuals or the contralateral knee. Statistical analysis was by Wilcoxon signed rank test and Spearman rank order correlation coefficient. RESULTS: JPS was impaired in ACL deficient knees. The mean (SD) errors in reproducing angles were 9.4 (3.1) degrees and 7.1 (2.3) degrees for the ACL deficient knee and control knee respectively (P < 0.0005). There was no improvement in JPS after rehabilitation (9.4 (3.1) degrees and 8.5 (3.2) degrees before and after rehabilitation respectively, P = 0.14). There was improvement as ascertained from the questionnaire (on admission 202 (32.1), after rehabilitation 243 (25.4), P < 0.0001) and functional activity testing (hop: on admission 148.7 (37.3) cm, after rehabilitation 169.8 (31.1) cm, P < 0.0005; figure of eight: on admission 48.4 (16.6) seconds, after rehabilitation 41.6 (3.4) seconds, P < 0.0001). Quadriceps strength improved (peak torque on admission 198.5 (58.9) Nm, after rehabilitation 210.5 (54.2) Nm, P < 0.05), but not hamstring strength (peak torque on admission 130.6 (28.1) Nm, after rehabilitation 135.5 (27.7) Nm, P = 0.24). JPS did not correlate with the functional activity tests (hop and figure of eight run), the responses to the questionnaire, or strength. There was no correlation between the responses to the questionnaire and functional activity tests or muscle strength. CONCLUSIONS: JPS was impaired in ACL deficient knees. Although knee stability improved with exercise therapy, there was no improvement in JPS. The role of JPS in the stability of ACL deficient knees remains unclear.
PMCID: PMC1332521  PMID: 9298555
7.  Effects of ACL reconstruction surgery on muscle activity of the lower limb during a jump-cut maneuver in males and females 
We compared muscle activity of the quadriceps, hamstring, and gastrocnemius muscles when ACL-intact (ACLINT) and ACL-reconstructed (ACLREC) male and female subjects performed a jump-cut task. Surface electromyography sensors were used to evaluate time to peak muscle activity and muscle activity ratios. Rectus femoris (RF) and vastus medialis (VM) peak timing was 71 ms and 78 ms earlier in ACLINT than in ACLREC subjects, respectively. Biceps femoris (BF) peak timing was 90 ms earlier in ACLINT than in ACLREC subjects and 75 ms earlier in females than in males. Medial gastrocnemius (MG) muscle peak timing was 77 ms earlier in ACLINT than in ACLREC subjects. Lateral gastrocnemius (LG) and MG muscle peak times were 106 ms and 87 ms earlier in females than in males, respectively. The RF, VM, BF and MG peaked later in ACLREC than in ACLINT subjects. There was evidence suggesting that the loading phase quadriceps:hamstring (quad:ham) muscle activity ratio was greater in ACLREC than in ACLINT subjects. Finally, the injury risk phase quad:ham muscle activity ratio was found to be 4.8 times greater in females than in males. In conclusion, there are differences in muscle activity related to ACL status and sex that could potentially help explain graft failure risk and the sex bias.
doi:10.1002/jor.22470
PMCID: PMC3808517  PMID: 23966333
ACL; Injury; Reconstruction; Muscle; EMG
8.  Treatment of Knee Osteoarthritis in Relation to Hamstring and Quadriceps Strength 
Journal of Physical Therapy Science  2013;25(11):1401-1405.
[Purpose] To assess the effect of hamstring and quadriceps strengthening exercises on pain intensity, gait velocity, maximum isometric strength, and activities of daily living of patients with knee osteoarthritis (OA). [Subjects and Methods] A total of 20 patients with knee OA, 50 to 65 years of age (57.65 ± 4.78 years), received hot packs, strengthening exercises for the quadriceps and the hamstring muscles and stretching exercises for hamstring muscles. Outcome measures included: the Western Ontario and McMaster Universities OA index questionnaire (WOMAC) scores for assessing health status and health outcomes of knee OA; self-reported pain intensity scores, measured using a visual analogue scale; the 50 ft walk test (a measure of gait velocity and function); and handheld dynamometry (a tool used to measure maximum isometric strength of knee extension and flexion). [Results] There was a significant difference between pre- and post-intervention measures of pain intensity, 50 ft walk times, hamstring strength, and quadriceps strength. Significant differences in WOMAC measures were also observed in the subscales of pain, stiffness and physical function, as well as WOMAC total scores. [Conclusion] Strengthening the hamstring muscles in addition to strengthening the quadriceps muscles proved to be beneficial for perceived knee pain, range of motion, and decreasing the limitation of functional performance of patients with knee OA.
doi:10.1589/jpts.25.1401
PMCID: PMC3881465  PMID: 24396198
Hamstring/quadriceps ratio; Knee pain; Osteoarthritis
9.  Vibration Therapy in Management of Delayed Onset Muscle Soreness (DOMS) 
Both athletic and nonathletic population when subjected to any unaccustomed or unfamiliar exercise will experience pain 24-72 hours postexercise. This exercise especially eccentric in nature caused primarily by muscle damage is known as delayed-onset muscle soreness (DOMS). This damage is characterized by muscular pain, decreased muscle force production, reduce range of motion and discomfort experienced. DOMS is due to microscopic muscle fiber tears. The presence of DOMS increases risk of injury.
A reduced range of motion may lead to the incapability to efficiently absorb the shock that affect physical activity. Alterations to mechanical motion may increase strain placed on soft tissue structures. Reduced force output may signal compensatory recruitment of muscles, thus leading to unaccustomed stress on musculature. Differences in strength ratios may also cause excessive strain on unaccustomed musculature. A range of interventions aimed at decreasing symptoms of DOMS have been proposed. Although voluminous research has been done in this regard, there is little consensus among the practitioners regarding the most effective way of treating DOMS.
Mechanical oscillatory motion provided by vibration therapy. Vibration could represent an effective exercise intervention for enhancing neuromuscular performance in athletes. Vibration has shown effectiveness in flexibility and explosive power. Vibration can apply either local area or whole body vibration. Vibration therapy improves muscular strength, power development, kinesthetic awareness, decreased muscle sore, increased range of motion, and increased blood flow under the skin. VT was effective for reduction of DOMS and regaining full ROM. Application of whole body vibration therapy in postexercise demonstrates less pressure pain threshold, muscle soreness along with less reduction maximal isometric and isokinetic voluntary strength and lower creatine kinase levels in the blood.
doi:10.7860/JCDR/2014/7323.4434
PMCID: PMC4127040  PMID: 25121012
DOMS; Management; Vibration therapy
10.  Isokinetic strength testing does not predict hamstring injury in Australian Rules footballers 
OBJECTIVE: To determine the relation of hamstring and quadriceps muscle strength and imbalance to hamstring injury using a prospective observational cohort study METHOD: A total of 102 senior male Australian Rules footballers aged 22.2 (3.6) years were tested at the start of a football season. Maximum voluntary concentric and eccentric torque of the hamstring and quadriceps muscles of both legs was assessed using a Kin-Com isokinetic dynamometer at angular velocities of 60 and 180 degrees/second. Twelve (11.8%) players sustained clinically diagnosed hamstring strains which caused them to miss one or more matches over the ensuing season. RESULTS: There were no significant differences for any of the isokinetic variables comparing the injured and non-injured legs in players with unilateral hamstring strains (n=9). Neither the injured nor the non-injured leg of injured players differed from the mean of left and right legs in non-injured players for any isokinetic variable. The hamstring to opposite hamstring ratios also did not differ between injured and non-injured players. A hamstring to opposite hamstring ratio of less than 0.90 and a hamstring to quadriceps ratio of less than 0.60 were not associated with an increased risk of hamstring injury. A significantly greater percentage of players who sustained a hamstring strain reported a history of hamstring strain compared with non-injured players (p=0.02). However, this was not related to muscle weakness or imbalance. CONCLUSIONS: Isokinetic muscle strength testing was not able to directly discriminate Australian Rules football players at risk for a hamstring injury. 



PMCID: PMC1756115  PMID: 9865403
11.  THE ACTIVITY PATTERN OF THE LUMBO‐PELVIC MUSCLES DURING PRONE HIP EXTENSION IN ATHLETES WITH AND WITHOUT HAMSTRING STRAIN INJURY 
ABSTRACT
Background:
Altered muscular activation pattern has been associated with musculoskeletal disorders. Some previous studies have demonstrated muscle weakness or tightness in athletes who have sustained hamstring (HAM) injuries. However, no study has clinically investigated the muscular activity pattern in subjects with HAM strain injuries.
Objective:
To investigate the activity pattern of the ipsilateral erector spinae (IES), contralateral erector spinae (CES), gluteus maximus (GM), and medial and lateral HAM muscles during the prone hip extension (PHE) test in athletes with and without history of HAM strain injury.
Design:
Cross‐sectional non‐experimental study design.
Participants:
A convenience sample of 20 soccer athletes participated in the study. Subjects were categorized into two groups: those with history of HAM strain injury (n=10, mean age = 22.6 ± 3.74) and without history of HAM strain (n =10, mean age = 22.45 ± 3.77).
Methods:
Three repetitions of the PHE were performed by each subject, and the electromyographic (EMG) outputs of the IES, CES, GM, and HAM muscles were recorded, processed and normalized to maximum voluntary electrical activity (MVE). Independent t‐tests were used for comparing activation means of each muscle between athletes with and without history of HAM strain injury.
Results:
There were significant differences in EMG activity of the GM (p= 0.04) and medial HAM (p = 0.01) between two groups. No significant difference was found in EMG signals of the IES (p= 0.26), CES (= 0.33) and lateral HAM (p= 0.58) between the two groups. Greater although non‐significant normalized EMG outputes of IES, CES and lateral HAM were seen in athletes with history of HAM strain compared to those without HAM strain.
Conclusion:
The findings of this study demonstrated greater normalized EMG activity of GM and medial HAM tested in athletes with history of HAM strain compared to those without HAM strain (altered activation pattern).
Level Of Evidence:
3a
PMCID: PMC4060308  PMID: 24944849
Electromyography; hamstring strain; movement pattern; prone hip extension
12.  Functional and Neuromuscular Changes in the Hamstrings After Drop Jumps and Leg Curls 
The purpose of this study was to use a holistic approach to investigate changes in jumping performance, kinaesthesia, static balance, isometric strength and fast stepping on spot during a 5-day recovery period, following an acute bout of damaging exercise consisted of drop jumps and leg curls, where specific emphasis was given on the hamstring muscles. Eleven young healthy subjects completed a series of highly intensive damaging exercises for their hamstring muscles. Prior to the exercise, and during the 5-day recovery period, the subjects were tested for biochemical markers (creatine kinase, aspartate aminotransferase, and lactate dehydrogenase), perceived pain sensation, physical performance (squat jump, counter movement jump, maximal frequency leg stamping, maximal isometric torque production and maximally explosive isometric torque production), kinaesthesia (active torque tracking) and static balance. We observed significant decreases in maximal isometric knee flexion torque production, the rate of torque production, and majority of the parameters for vertical jump performance. No alterations were found in kinaesthesia, static balance and fast stepping on spot. The highest drop in performance and increase in perceived pain sensation generally occurred 24 or 48 hours after the exercise. Damaging exercise substantially alters the neuromuscular functions of the hamstring muscles, which is specifically relevant for sports and rehabilitation experts, as the hamstrings are often stretched to significant lengths, in particular when the knee is extended and hip flexed. These findings are practically important for recovery after high-intensity trainings for hamstring muscles.
Key PointsHamstring function is significantly reduced following specifically damaging exercise.It fully recovers 120 hours after the exercise.Prevention of exercise-induced muscle damage is cruicial for maintaining normal training regime.
PMCID: PMC3772585  PMID: 24149148
Isometric strength; stamping; balance; kinaesthesia; DOMS; EIMD
13.  Effects of rest interval on isokinetic strength and functional performance after short-term high intensity training. 
OBJECTIVES: The ability to maximally generate active muscle tension during resistance training has been established to be a primary determinant for strength development. The influence of intrasession rest intervals may have a profound effect on strength gains subsequent to short-term high intensity training. The purpose of this study was to examine the effects of rest interval on strength and functional performance after four weeks of isokinetic training. METHODS: Fifteen healthy college aged individuals were randomly assigned to either a short rest interval group (group 1, n = 8) or a long rest interval group (group 2, n = 7). Subjects were evaluated for quadriceps and hamstring isokinetic strength at 60 (five repetitions) and 180 (30 repetitions) degrees/second and functional performance with the single leg hop for distance test. One leg of each subject was randomly assigned to a four week, three days/week isokinetic strength training programme for concentric knee extension and flexion performed at 90 degrees/second. Subjects in group 1 received a 40 second rest interval in between exercise sets, whereas subjects in group 2 received a 160 second rest period. RESULTS: A two factor analysis of variance for the pre-test--post-test gain scores (%) showed significantly greater improvements for isokinetic hamstring total work and average power at 180 degrees/second for the trained limb of subjects in group 2 than their contralateral non-trained limb and the subjects in group 1. Significantly greater improvements for the single leg hop for distance were also found for the trained limbs of subjects in both groups as compared with the non-trained limbs. CONCLUSIONS: The findings indicate that a relatively longer intrasession rest period resulted in a greater improvement in hamstring muscle strength during short term high intensity training.
PMCID: PMC1332526  PMID: 9298559
14.  Acute Effects of Two Different Warm-Up Protocols on Flexibility and Lower Limb Explosive Performance in Male and Female High Level Athletes 
This study examined the effects of two different warm-up protocols on lower limb power and flexibility in high level athletes. Twenty international level fencers (10 males and 10 females) performed two warm-up protocols that included 5-min light jogging and either short (15s) or long (45s) static stretching exercises for each of the main leg muscle groups (quadriceps, hamstrings and triceps surae), followed by either 3 sets of 3 (short stretching treatment), or 3 sets of 5 tuck jumps (long stretching treatment), in a randomized crossover design with one week between treatments. Hip joint flexion was measured with a Lafayette goniometer before and after the 5-min warm-up, after stretching and 8 min after the tuck jumps, while counter movement jump (CMJ) performance was evaluated by an Ergojump contact platform, before and after the stretching treatment, as well as immediately after and 8 minutes after the tuck jumps. Three way ANOVA (condition, time, gender) revealed significant time (p < 0.001) and gender (p < 0.001) main effects for hip joint flexion, with no interaction between factors. Flexibility increased by 6. 8 ± 1.1% (p < 0.01) after warm-up and by another 5.8 ± 1.6% (p < 0.01) after stretching, while it remained increased 8 min after the tuck jumps. Women had greater ROM compared with men at all time points (125 ± 8° vs. 94 ± 4° p<0.01 at baseline), but the pattern of change in hip flexibility was not different between genders. CMJ performance was greater in men compared with women at all time points (38.2 ± 1.9 cm vs. 29.8 ± 1.2 cm p < 0.01 at baseline), but the percentage of change CMJ performance was not different between genders. CMJ performance remained unchanged throughout the short stretching protocol, while it decreased by 5.5 ± 0.9% (p < 0.01) after stretching in the long stretching protocol However, 8 min after the tuck jumps, CMJ performance was not different from the baseline value (p = 0.075). In conclusion, lower limb power may be decreased after long periods of stretching, but performance of explosive exercises may reverse this phenomenon.
Key points
Stretching of the main leg muscle groups for 45 s results in a relatively large decrease (by 5.5%) in subsequent jumping performance
Stretching of the main leg muscle groups for only 15 s results in an increase in flexibility similar to that of the longer duration stretching (by 12.6%), with no change in subsequent jumping performance
Performance of a PAP exercise such as tuck jumps may reverse the negative effects of long duration stretching on leg muscle power. However, jumping performance is not increased above baseline
Speed/power athletes should be advised against using long duration stretching. The number of repetitions of a PAP exercise such as the tuck jumps, should be further examined in order to induce an increase in explosive performance during competition
PMCID: PMC3763313  PMID: 24150077
Countermovement jump; stretching; post-activation potentiation; fencing
15.  Evaluating the Influence of Massage on Leg Strength, Swelling, and Pain Following a Half-Marathon 
Journal of Sports Science & Medicine  2004;3(YISI 1):37-43.
Massage therapy is commonly used following endurance running races with the expectation that it will enhance post-run recovery of muscle function and reduce soreness. A limited number of studies have reported little or no influence of massage therapy on post-exercise muscle recovery. However, no studies have been conducted in a field setting to assess the potential for massage to influence muscle recovery following an actual endurance running race. To evaluate the potential for repeated massage therapy interventions to influence recovery of quadriceps and hamstring muscle soreness, recovery of quadriceps and hamstring muscle strength and reduction of upper leg muscle swelling over a two week recovery period following an actual road running race. Twelve adult recreational runners (8 male, 4 female) completed a half marathon (21.1 km) road race. On days 1,4, 8, and 11 post-race, subjects received 30 minutes of standardized massage therapy performed by a registered massage therapist on a randomly assigned massage treatment leg, while the other (control) leg received no massage treatment. Two days prior to the race (baseline) and preceding the treatments on post-race days 1, 4, 8, and 11 the following measures were conducted on each of the massage and control legs: strength of quadriceps and hamstring muscles, leg swelling, and soreness perception. At day 1, post-race quadriceps peak torque was significantly reduced (p < 0.05), and soreness and leg circumference significantly elevated (p < 0.05) relative to pre-race values with no difference between legs. This suggested that exercise-induced muscle disruption did occur. Comparing the rate of return to baseline measures between the massaged and control legs, revealed no significant differences (p > 0.05). All measures had returned to baseline at day 11. Massage did not affect the recovery of muscles in terms of physiological measures of strength, swelling, or soreness. However, questionnaires revealed that 7 of the 12 participants perceived that the massaged leg felt better upon recovery.
Key PointsMassage does not appear to affect physiological indices of muscle recovery post exercise.Massage does appear to positively influence perceptions of recovery.More research needs to be completed on the purported benefits of massage.
PMCID: PMC3990931  PMID: 24778552
Recovery; running; perception; massage
16.  OFF‐SEASON TRAINING HABITS AND PRESEASON FUNCTIONAL TEST MEASURES OF DIVISION III COLLEGIATE ATHLETES: A DESCRIPTIVE REPORT 
Purpose/Background:
Division III (D III) collegiate coaches are challenged to assess athletic readiness and condition their athletes during the preseason. However, there are few reports on off‐season training habits and normative data of functional assessment tests among D III athletes. The purpose of this study was to examine off‐season training habits of D III athletes and their relationships to the standing long jump (SLJ) and single‐leg hop (SLH) tests.
Methods:
One‐hundred and ninety‐three athletes (110 females, age 19.1 ± 1.1 y; 83 males, age 19.5 ± 1.3 y) were tested prior to the start of their sports seasons. Athletes reported their off‐season training habits (weightlifting, cardiovascular exercise, plyometric exercise, and scrimmage) during the six weeks prior to the preseason. Athletes also performed three maximal effort SLJs and three SLHs.
Results:
Male athletes reported training more hours per exercise category than their female counterparts. Mean SLJ distances (normalized to height) were 0.79 ± 0.10 for females and 0.94 ± 0.12 for males. Mean SLH distances for female athletes' right and left limbs were 0.66 (± 0.10) and 0.65 (± 0.10), respectively. Mean SLH distances for male athletes' right and left limbs were 0.75 (± 0.13) and 0.75 (± 0.12), respectively. Several significant differences between off‐season training habits and functional test measures were found for both sexes: males [SLJ and weightlifting (p = 0.04); SLH and weightlifting (p = 0.04), plyometrics (p = 0.05)]; females [SLJ and plyometrics (p = 0.04); SLH and scrimmage (p = 0.02)].
Conclusion:
This study provides normative data for off‐season training habits and preseason functional test measures in a D III athlete population. Greater SLJ and SLH measures were associated with increased time during off‐season training.
Clinical Relevance:
The findings between functional tests and off‐season training activities may be useful for sports medicine professionals and strength coaches when designing their preseason training programs.
Level of Evidence:
4
PMCID: PMC4127507  PMID: 25133073
college; field test; functional test; single‐leg hop; standing long jump
17.  Contribution of Hamstring Fatigue to Quadriceps Inhibition Following Lumbar Extension Exercise 
The purpose of this study was to determine the contribution of hamstrings and quadriceps fatigue to quadriceps inhibition following lumbar extension exercise. Regression models were calculated consisting of the outcome variable: quadriceps inhibition and predictor variables: change in EMG median frequency in the quadriceps and hamstrings during lumbar fatiguing exercise. Twenty-five subjects with a history of low back pain were matched by gender, height and mass to 25 healthy controls. Subjects performed two sets of fatiguing isometric lumbar extension exercise until mild (set 1) and moderate (set 2) fatigue of the lumbar paraspinals. Quadriceps and hamstring EMG median frequency were measured while subjects performed fatiguing exercise. A burst of electrical stimuli was superimposed while subjects performed an isometric maximal quadriceps contraction to estimate quadriceps inhibition after each exercise set. Results indicate the change in hamstring median frequency explained variance in quadriceps inhibition following the exercise sets in the history of low back pain group only. Change in quadriceps median frequency explained variance in quadriceps inhibition following the first exercise set in the control group only. In conclusion, persons with a history of low back pain whose quadriceps become inhibited following lumbar paraspinal exercise may be adapting to the fatigue by using their hamstring muscles more than controls.
Key PointsA neuromuscular relationship between the lumbar paraspinals and quadriceps while performing lumbar extension exercise may be influenced by hamstring muscle fatigue.QI following lumbar extension exercise in persons with a history of LBP group may involve significant contribution from the hamstring muscle group.More hamstring muscle contribution may be a necessary adaptation in the history of LBP group due to weaker and more fatigable lumbar extensors.
PMCID: PMC3818676  PMID: 24198683
Superimposed burst technique; electromyography; spectral median frequency; correlation and regression; low back pain
18.  A Progressive 5-Week Exercise Therapy Program Leads to Significant Improvement in Knee Function Early After Anterior Cruciate Ligament Injury 
STUDY DESIGN
Prospective cohort study without a control group.
OBJECTIVES
Firstly, to present our 5-week progressive exercise therapy program in the early stage after anterior cruciate ligament (ACL) injury. Secondly, to evaluate changes in knee function after completion of the program for patients with ACL injury in general and also when classified as potential copers or noncopers, and, finally, to examine potential adverse events.
BACKGROUND
Few studies concerning early-stage ACL rehabilitation protocols exist. Consequently, little is known about the tolerance for, and outcomes from, short-term exercise therapy programs in the early stage after injury.
METHODS
One-hundred patients were included in a 5-week progressive exercise therapy program, within 3 months after injury. Knee function before and after completion of the program was evaluated from isokinetic quadriceps and hamstrings muscle strength tests, 4 single-leg hop tests, 2 different self-assessment questionnaires, and a global rating of knee function. A 2-way mixed-model analysis of variance was conducted to evaluate changes from pretest to posttest for the limb symmetry index for muscle strength and single-leg hop tests, and the change in scores for the patient-reported questionnaires. In addition, absolute values and the standardized response mean for muscle strength and single-leg hop tests were calculated at pretest and posttest for the injured and uninjured limb. Adverse events during the 5-week period were recorded.
RESULTS
The progressive 5-week exercise therapy program led to significant improvements (P<.05) in knee function from pretest to posttest both for patients classified as potential copers and noncopers. Standardized response mean values for changes in muscle strength and single-leg hop performance from pretest to posttest for the injured limb were moderate to strong (0.49–0.84), indicating the observed improvements to be clinically relevant. Adverse events occurred in 3.9% of the patients.
CONCLUSION
Short-term progressive exercise therapy programs are well tolerated and should be incorporated in early-stage ACL rehabilitation, either to improve knee function before ACL reconstruction or as a first step in further nonoperative management.
doi:10.2519/jospt.2010.3345
PMCID: PMC3158986  PMID: 20710097
ACL; adverse events; copers; hop tests; noncopers
19.  Mechanisms of quadriceps muscle weakness in knee joint osteoarthritis: the effects of prolonged vibration on torque and muscle activation in osteoarthritic and healthy control subjects 
Arthritis Research & Therapy  2011;13(5):R151.
Introduction
A consequence of knee joint osteoarthritis (OA) is an inability to fully activate the quadriceps muscles, a problem termed arthrogenic muscle inhibition (AMI). AMI leads to marked quadriceps weakness that impairs physical function and may hasten disease progression. The purpose of the present study was to determine whether γ-loop dysfunction contributes to AMI in people with knee joint OA.
Methods
Fifteen subjects with knee joint OA and 15 controls with no history of knee joint pathology participated in this study. Quadriceps and hamstrings peak isometric torque (Nm) and electromyography (EMG) amplitude were collected before and after 20 minutes of 50 Hz vibration applied to the infrapatellar tendon. Between-group differences in pre-vibration torque were analysed using a one-way analysis of covariance, with age, gender and body mass (kg) as the covariates. If the γ-loop is intact, vibration should decrease torque and EMG levels in the target muscle; if dysfunctional, then torque and EMG levels should not change following vibration. One-sample t tests were thus undertaken to analyse whether percentage changes in torque and EMG differed from zero after vibration in each group. In addition, analyses of covariance were utilised to analyse between-group differences in the percentage changes in torque and EMG following vibration.
Results
Pre-vibration quadriceps torque was significantly lower in the OA group compared with the control group (P = 0.005). Following tendon vibration, quadriceps torque (P < 0.001) and EMG amplitude (P ≤0.001) decreased significantly in the control group but did not change in the OA group (all P > 0.299). Hamstrings torque and EMG amplitude were unchanged in both groups (all P > 0.204). The vibration-induced changes in quadriceps torque and EMG were significantly different between the OA and control groups (all P < 0.011). No between-group differences were observed for the change in hamstrings torque or EMG (all P > 0.554).
Conclusions
γ-loop dysfunction may contribute to AMI in individuals with knee joint OA, partially explaining the marked quadriceps weakness and atrophy that is often observed in this population.
doi:10.1186/ar3467
PMCID: PMC3308081  PMID: 21933392
20.  H:Q Ratios and Bilateral Leg Strength in College Field and Court Sports Players 
Journal of Human Kinetics  2012;33:63-71.
One of the key components in sports injury prevention is the identification of imbalances in leg muscle strength. However, different leg muscle characteristics may occur in large playing area (field) sports and small playing area (court) sports, which should be considered in regular injury prevention assessment. This study examined the isokinetic hamstrings-to-quadriceps (H:Q) ratio and bilateral leg strength balance in 40 male college (age: 23.4 ± 2.5 yrs) team sport players (field sport = 23, soccer players; court sport = 17, volleyball and basketball players). Five repetitions of maximal knee concentric flexion and concentric extension were performed on an isokinetic dynamometer at two speeds (slow: 60°·s−1 and fast: 300°·s−1) with 3 minutes rest between tests. Both legs were measured in counterbalanced order with the dominant leg being determined as the leg used to kick a ball. The highest concentric peak torque values (Nm) of the hamstrings and quadriceps of each leg were analyzed after body mass normalization (Nm·kg−1). Court sport players showed significantly weaker dominant leg hamstrings muscles at both contraction speeds (P < 0.05). The H:Q ratio was significantly larger in field players in their dominant leg at 60°·s−1 (P < 0.001), and their non-dominant leg at 300°·s−1 (P < 0.001) respectively. Sport-specific leg muscle strength was evident in college players from field and court sports. These results suggest the need for different muscle strength training and rehabilitation protocols for college players according to the musculature requirements in their respective sports.
doi:10.2478/v10078-012-0045-1
PMCID: PMC3588678  PMID: 23487043
asymmetry; soccer; volleyball; basketball; muscle imbalance; leg strength
21.  The Carry-Over Effects of Diathermy and Stretching in Developing Hamstring Flexibility 
Journal of Athletic Training  2002;37(1):37-42.
Objective: To compare the effects of low-load, short-duration stretching with or without high-intensity, pulsed short-wave diathermy on hamstring flexibility.
Design and Setting: We used a single-blind, repeated-measures design (pretest and posttest for all treatments) that included a placebo. The 3 independent variables were treatment mode, pretest and posttest measurements, and day. Treatment mode had 3 levels: diathermy and stretching, stretching alone, and control. The dependent variable was range of motion. Subjects were randomly assigned to the diathermy and stretching, stretching-only, or control group. Subjects were treated and tested each day (at approximately the same time) for 5 days, with a follow-up test administered 72 hours later. Hamstring flexibility was tested using a sit-and-reach box before and after each treatment. Diathermy and stretching subjects received a 15-minute diathermy treatment on the right hamstring at a setting of 7000 pulses per second, with an average pulse width of 95 μsec. Stretching-only subjects received a 15-minute sham diathermy treatment. Both diathermy and stretching and stretching-only subjects then performed three 30-second stretches (short duration) before being retested. Control subjects lay prone for 15 minutes before being retested.
Subjects: Thirty-seven healthy college students (11 men, 26 women, age = 20.46 ± 1.74 years) volunteered.
Measurements: Hamstring flexibility was measured using a sit-and-reach box before and after each treatment.
Results: The average increases in hamstring flexibility over the 5 treatment days for the diathermy and stretching, stretching-only, and control groups were 6.06 cm (19.6%), 5.27 cm (19.7%), and 3.38 cm (10.4%), respectively. Three days later (after no treatment), the values for the diathermy and stretching, stretching-only, and control groups were 8.27 cm (26.7%), 6.83 cm (25.3%), and 4.15 cm (14.2%), respectively. No significant differences in hamstring flexibility were noted among the groups.
Conclusions: Diathermy and short-duration stretching were no more effective than short-duration stretching alone at increasing hamstring flexibility. The effects of diathermy with longer stretching times need to be researched.
PMCID: PMC164306  PMID: 12937442
heat; stretch; injury treatment
22.  Rapid Hamstrings/Quadriceps Strength Capacity in Professional Soccer Players with Different Conventional Isokinetic Muscle Strength Ratios 
Muscle strength imbalance can be an important factor in hamstrings muscle strain. A hamstrings/quadriceps (H/Q) strength ratio based on concentric peak torque values (Hcon:Qcon) has traditionally been used to describe the potential for knee-joint destabilization. Because certain standard actions in soccer are explosive, the analysis of the H/Q strength ratio based on the rate of torque development (Hrtd:Qrtd) might also be useful in the evaluation of joint stability. The objective of this study was to compare the Hrtd:Qrtd between professional soccer players with heterogeneous values of Hcon:Qcon. Thirty-nine professional soccer players took part in the following procedures on different days: 1) Familiarization session with the isokinetic dynamometer, and 2) Two maximal isometric actions and five maximal concentric actions at 60°·s-1 for hamstrings (H) and quadriceps (Q). Participants were ranked according to their Hcon:Qcon ratio. The median third was excluded to form a high torque group (HTG), and a low torque group (LTG). Peak isometric (H) and concentric (H and Q) torques and rate of torque development (H) were significantly greater in the HTG group. Similarly, Hcon:Qcon (0.68 ± 0.02 vs. 0.52 ± 0.03) and Hrtd:Qrtd (0.54 ± 0.12 vs. 0.43 ± 0.16) were significantly greater in the HTG group than in the LTG group. There was no significant correlation between Hcon:Qcon and Hrtd:Qrtd. It can be concluded that Hcon:Qcon and Hrtd:Qrtd are determined, but not fully defined, by shared putative physiological mechanisms. Thus, the physiologic and clinical significance of Hcon:Qcon and Hrtd:Qrtd to an athlete’s individual evaluation might be different.
Key pointsSoccer players with high (0.66-0.70) and low (0.50-0.54) conventional concentric hamstrings:quadriceps ratios (Hcon:Qcon) tend to demonstrate similar profiles (i.e., high and low, respectively) in their rate of the torque development H/Q ratio (Hrtd:Qrtd).The lack of a significant relationship between Hcon:Qcon and Hrtd:Qrtd suggests that these ratios are determined, but not fully defined, by shared putative physiological mechanisms.Preseason screening programs that monitor hamstrings:quadriceps ratios should recognize that the physiologic and clinical significance of Hcon:Qcon and Hrfd:Qrfd to an athlete’s individual evaluation might be different.
PMCID: PMC3737945  PMID: 24149348
Muscular torque; isometric action; injury
23.  Comparative Study of Hamstring and Quadriceps Strengthening Treatments in the Management of Knee Osteoarthritis 
[Purpose] Osteoarthritis (OA) of the knee is the most common form of joint disease. It is one of the major causes of impaired function that reduces quality of life (QOL) worldwide. The purpose of this study was to compare exercise treatments for hamstring and quadriceps strength in the management of knee osteoarthritis. [Subjects and Methods] Forty patients with OA knee, aged 50–65 years were divided into 2 groups. The first group (57.65±4.78 years) received hot packs and performed strengthening exercises for the quadriceps and hamstring, and stretching exercises for the hamstring. The second group (58.15±5.11 years) received hot packs and performed strengthening exercises for only the quadriceps, and stretching exercise for the hamstring. Outcome measures were the WOMAC (Western Ontario and McMaster Universities OA index questionnaire), Visual Analogue Scale (VAS) assessment of pain, the Fifty-Foot Walk Test (FWS), and Handheld dynamometry. [Results] There was a significant difference between the groups. The first group showed a more significant result than the second group. [Conclusion] Strengthening of the hamstrings in addition to strengthening of the quadriceps was shown to be beneficial for improving subjective knee pain, range of motion and decreasing the limitation of functional performance of patients with knee osteoarthritis.
doi:10.1589/jpts.26.817
PMCID: PMC4085199  PMID: 25013274
Strengthening; Stretching; Pain
24.  Effects of Whole-Body Vibration Training on Bone-Free Lean Body Mass and Muscle Strength in Young Adults 
Resistance training with whole-body vibration (WBV) is becoming increasingly popular as an alternative to conventional resistance training or as supplementary training. Despite its growing popularity, the specific effects of WBV training on muscle morphology, strength, and endurance are not well understood, particularly in young adults. The aim of this study was to determine the effects of WBV training on bone-free lean body mass (BFLBM), and maximal muscle strength and endurance in healthy, untrained, young individuals. Eighteen healthy men and women (21-39 years) were randomly assigned to either a body-weight exercise with WBV (VT) group or a control exercise group without WBV (CON). Participants performed eight exercises per 40- min session on a vibration platform (VT group, frequency = 30-40 Hz; amplitude = 2 mm) twice weekly for 12 weeks. Anthropometry, total and regional BFLBM (trunks, legs, and arms) measured by dual- energy X-ray absorptiometry, and muscle strength and endurance measured by maximal isometric lumbar extension strength, maximal isokinetic knee extension and flexion strength, and the number of sit- ups performed were recorded and compared. Two-way repeated-measures ANOVA revealed no significant changes between the groups in any of the measured variables. We conclude that 12 weeks of body weight vibration exercise compared to body weight exercise alone does not provide meaningful changes to BFLBM or muscle performance in healthy young adults.
Key pointsA randomized controlled trial was conducted to investigate the effects of body-weight exercise combined with whole-body vibration on bone-free lean body mass and maximal muscle strength and endurance in healthy young individuals.Body-weight exercises for lower extremities and trunk muscles were performed twice weekly for 12 weeks.Participants in the exercise with whole-body vibration group increased the vibration frequency from 30, 35, to 40 Hz at a constant amplitude of 2 mm during the trial.A 12-week body-weight exercise program with whole-body vibration did not significantly increase bone-free lean body mass in healthy young individuals, and no additional increases in maximal muscle strength and endurance were observed.
PMCID: PMC3737898  PMID: 24149301
vibration; exercise; lean body mass; young; untrained
25.  Influence of vibration on delayed onset of muscle soreness following eccentric exercise 
Delayed onset muscle soreness (DOMS), which may occur after eccentric exercise, may cause some reduction in ability in sport activities. For this reason, several studies have been designed on preventing and controlling DOMS. As vibration training (VT) may improve muscle performance, we designed this study to investigate the effect of VT on controlling and preventing DOMS after eccentric exercise.
Methods
Fifty healthy non‐athletic volunteers were assigned randomly into two experimental, VT (n = 25) and non‐VT (n = 25) groups. A vibrator was used to apply 50 Hz vibration on the left and right quadriceps, hamstring and calf muscles for 1 min in the VT group, while no vibration was applied in the non‐VT group. Then, both groups walked downhill on a 10° declined treadmill at a speed of 4 km/hour. The measurements included the isometric maximum voluntary contraction force (IMVC) of left and right quadriceps muscles, pressure pain threshold (PPT) 5, 10 and 15 cm above the patella and mid‐line of the calf muscles of both lower limbs before and the day after treadmill walking. After 24 hours, the serum levels of creatine‐kinase (CK), and DOMS level by visual analogue scale were measured.
Results
The results showed decreased IMVC force (P = 0.006), reduced PPT (P = 0.0001) and significantly increased mean of DOMS and CK levels in the non‐VT group, compared to the VT group (P = 0.001).
Conclusion
A comparison by experimental groups indicates that VT before eccentric exercise may prevent and control DOMS. Further studies should be undertaken to ascertain the stability and effectiveness of VT in athletics.
doi:10.1136/bjsm.2006.031278
PMCID: PMC2465226  PMID: 17138635
vibration training; eccentric exercise; DOMS

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