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1.  The Effects of Exercise on Decreasing Pain and Increasing Function in Patients With Patellofemoral Pain Syndrome 
Sports Health  2012;4(3):205-210.
Exercise or rest is commonly prescribed as treatment for patellofemoral pain syndrome.
Study Selection:
This study is based on Level I or II research studies examining the effects of exercise and rest on decreasing pain (visual analog scale) and increasing function (Kujala Scoring Questionnaire) using human participants. Articles were limited to those printed in English from PubMed (1966–September 2010), CINAHL (1982–September 2010), and SPORTDiscus (1972–September 2010).
Data Extraction:
Weighted aggregate effect sizes and 95% confidence intervals were calculated from means and standard deviations extracted from 10 studies, resulting in an analysis of 433 patients.
A very large effect for exercise was found for patient-reported functional outcomes (d = 2.19) and perceived pain (d = −1.24) in treated patients, which were larger than functional outcomes (d = 0.77) and pain (d = −0.14) in controls. Short-term follow-up of 191 patients from 4 data sets in 2 studies revealed a large effect for functional outcomes (d = 1.04) and pain (d = −0.82) in patients who performed an exercise intervention. One study reported moderate effect sizes for functional outcomes (d = 0.59) and pain (d = −0.35) at 3 months postintervention.
Exercise is the more effective treatment for immediate decrease in pain and increase in function although these differences appear to be less distinguishable over time.
PMCID: PMC3435930  PMID: 23016088
visual analogue scale; Kujala Scoring Questionnaire
2.  Microvascular Perfusion and Intramuscular Temperature of the Calf During Cooling 
To examine how the microvascularity of the gastrocnemius changed after a cryotherapy intervention based on subcutaneous tissue thickness. A secondary purpose was to compare intramuscular temperature change to subcutaneous tissue thickness.
This was a single-blinded crossover study; each subject received both conditions (cryotherapy or sham). Subjects had baseline measurements of blood flow, blood volume, and intramuscular temperature recorded at 1cm into the muscle belly of the medial gastrocnemius. The randomized condition was applied for 10, 25, 40, or 60min depending on subcutaneous tissue thickness. Immediate post treatment microvascular measures were taken. After a designated rewarm period, again based on subcutaneous tissue thickness, measurements were retaken. At least 48 hours separated the two conditions.
There were significant condition by time interactions for blood flow (p=0.01), blood volume (p=0.022), and intramuscular temperature (p<0.001). For blood flow and volume, the cryotherapy condition maintained baseline levels, while the sham condition increased at immediate-post treatment and rewarm. For intramuscular temperature, the cryotherapy condition caused a decrease in intramuscular temperature from baseline compared to no change in the sham condition from baseline. Intramuscular temperature change was significantly correlated to subcutaneous tissue thickness (r=.49; p=0.05).
Cryotherapy did not decrease blood flow and blood volume from resting levels, even though the intramuscular temperature decreased. An intramuscular change of 7–9°C may not be cold enough to cause local vasoconstriction.
PMCID: PMC3295862  PMID: 21988932
Contrast-enhanced ultrasound; cryotherapy; skeletal muscle; thermocouple
3.  Lower Extremity Neuromuscular Control Immediately After Fatiguing Hip-Abduction Exercise 
Journal of Athletic Training  2011;46(6):607-614.
Fatigue of the gluteus medius (GMed) muscle might be associated with decreases in postural control due to insufficient pelvic stabilization. Men and women might have different muscular recruitment patterns in response to GMed fatigue.
To compare postural control and quality of movement between men and women after a fatiguing hip-abduction exercise.
Descriptive laboratory study.
Controlled laboratory.
Patients or Other Participants:
Eighteen men (age = 22 ± 3.64 years, height = 183.37 ± 8.30 cm, mass = 87.02 ±12.53 kg) and 18 women (age = 22 ± 3.14, height = 167.65 ± 5.80 cm, mass = 66.64 ± 10.49 kg) with no history of low back or lower extremity injury participated in our study.
Participants followed a fatiguing protocol that involved a side-lying hip-abduction exercise performed until a 15% shift in electromyographic median frequency of the GMed was reached.
Main Outcome Measure(s):
Baseline and postfatigue measurements of single-leg static balance, dynamic balance, and quality of movement assessed with center-of-pressure measurements, the Star Excursion Balance Test, and lateral step-down test, respectively, were recorded for the dominant lower extremity (as identified by the participant).
We observed no differences in balance deficits between sexes (P > .05); however, we found main effects for time with all of our postfatigue outcome measures (P ≤ .05).
Our findings suggest that postural control and quality of movement were affected negatively after a GMed-fatiguing exercise. At similar levels of local muscle fatigue, men and women had similar measurements of postural control.
PMCID: PMC3418937  PMID: 22488185
gluteus medius muscle; postural control; balance
4.  Quadriceps Function After Exercise in Patients with Anterior Cruciate Ligament–Reconstructed Knees Wearing Knee Braces 
Journal of Athletic Training  2011;46(6):615-620.
Knee braces and neoprene sleeves are commonly worn by people with anterior cruciate ligament reconstructions (ACLRs) during athletic activity. How knee braces and sleeves affect muscle activation in people with ACLRs is unclear.
To determine the effects of knee braces and neoprene knee sleeves on the quadriceps central activation ratio (CAR) before and after aerobic exercise in people with ACLRs.
Crossover study.
Patients or Other Participants:
Fourteen people with a history of ACLR (9 women, 5 men: age = 23.61 ± 4.44 years, height = 174.09 ± 9.82 cm, mass = 75.35 ± 17.48 kg, months since ACLR = 40.62 ± 20.41).
During each of 3 sessions, participants performed a standardized aerobic exercise protocol on a treadmill. The independent variables were condition (brace, sleeve, or control) and time (baseline, pre-exercise with brace, postexercise with brace, postexercise without brace).
Main Outcome Measure(s):
Normalized torque measured during a maximal voluntary isometric contraction (TMVIC) and CAR were measured by a blinded assessor using the superimposed burst technique. The CAR was expressed as a percentage of full muscle activation. The quadriceps CAR and TMVIC were measured 4 times during each session: baseline, pre-exercise with brace, postexercise with brace, and postexercise without brace.
Immediately after the application of the knee brace, TMVIC decreased (P = .01), but no differences between bracing conditions were observed. We noted reduced TMVIC and CAR (P < .001) after exercise, both with and without the brace. No differences were seen between bracing conditions after aerobic exercise.
The decrease in TMVIC immediately after brace application was not accompanied by differences between bracing conditions. Wearing a knee brace or neoprene sleeve did not seem to affect the deterioration of quadriceps function after aerobic exercise.
PMCID: PMC3418938  PMID: 22488186
neuromuscular function; aerobic exercise; central activation ratio
5.  Electrode Type and Placement Configuration for Quadriceps Activation Evaluation 
Journal of Athletic Training  2011;46(6):621-628.
The ability to accurately estimate quadriceps voluntary activation is an important tool for assessing neuromuscular function after a variety of knee injuries. Different techniques have been used to assess quadriceps volitional activation, including various stimulating electrode types and electrode configurations, yet the optimal electrode types and configurations for depolarizing motor units in the attempt to assess muscle activation are unknown.
To determine whether stimulating electrode type and configuration affect quadriceps central activation ratio (CAR) and percentage-of-activation measurements in healthy participants.
Crossover study.
Research laboratory.
Patients and Other Participants:
Twenty participants (13 men, 7 women; age = 26 ± 5.3 years, height = 173.85 ± 7.3 cm, mass = 77.37 ± 16 kg) volunteered.
All participants performed 4 counter-balanced muscle activation tests incorporating 2 different electrode types (self-adhesive, carbon-impregnated) and 2 electrode configurations (vastus, rectus).
Main Outcome Measure(s):
Quadriceps activation was calculated with the CAR and percentage-of-activation equations, which were derived from superimposed burst and resting torque measurements.
No differences were found between conditions for CAR and percentage-of-activation measurements, whereas resting twitch torque was higher in the rectus configuration for both self-adhesive (216 ± 66.98 Nm) and carbon-impregnated (209.1 ± 68.22 Nm) electrodes than in the vastus configuration (209.5 ± 65.5 Nm and 204 ± 62.7 Nm, respectively) for these electrode types (F1,19 = 4.87, P = .04). In addition, resting twitch torque was greater for both electrode configurations with self-adhesive electrodes than with carbon-impregnated electrodes (F1,19 = 9.33, P = .007). Bland-Altman plots revealed acceptable mean differences for agreement between electrode type and configuration for CAR and percentage of activation, but limits of agreement were wide.
Although these electrode configurations and types might not necessarily be able to be used interchangeably, differences in electrode type and configuration did not seem to affect CAR and percentage-of-activation outcome measures.
PMCID: PMC3418939  PMID: 22488187
burst superimposition; interpolated twitch technique; central activation ratio; knee; motor neurons
6.  Neuromuscular Changes After Aerobic Exercise in People with Anterior Cruciate Ligament– Reconstructed Knees 
Journal of Athletic Training  2011;46(5):476-483.
Anterior cruciate ligament (ACL) reconstructions are common, especially in young, active people. The lower extremity neuromuscular adaptations seen after aerobic exercise provide information about how previously injured patients perform and highlight deficits and, hence, areas for focused treatment. Little information is available about neuromuscular performance after aerobic exercise in people with ACL reconstructions.
To compare dynamic balance, gluteus medius muscle activation, vertical jump height, and hip muscle strength after aerobic exercise in people with ACL-reconstructed knees.
Case-control study.
Research laboratory.
Patients or Other Participants:
Of 34 recreationally active volunteers, 17 had a unilateral primary ACL reconstruction at least 2 years earlier and 17 were matched controls.
All participants performed 20 minutes of aerobic exercise on a treadmill.
Main Outcome Measure(s):
We recorded dynamic, single-legged balance electromyographic gluteus medius muscle activation, single-legged vertical jump height, and maximum isometric strength for hip abduction, extension, and external rotation preexercise and postexercise.
Participants with ACL reconstructions exhibited shorter reach distances during dynamic balance tasks, indicating poorer dynamic balance, and less gluteus medius muscle electromyographic activation. Reductions in hip abduction and extension strength after exercise were noted in all participants; however, those with ACL reconstructions displayed greater hip extensor strength loss after aerobic exercise than did the control group.
Neuromuscular changes after aerobic exercise exist in both patients with ACL reconstructions and controls. The former group may experience greater deficits in hip extensor strength after aerobic exercise. Reduced reach distances in people with ACL reconstructions may represent a protective mechanism against excessive tibiofemoral rotation during dynamic balance. Clinicians should identify weaknesses in the resting state and after aerobic exercise in recreationally active patients and those with ACL reconstructions.
PMCID: PMC3418953  PMID: 22488134
skeletal muscle adaptations; fatigue; strength; isometric activity; isokinetic activity
7.  Reduced Quadriceps Activation After Lumbar Paraspinal Fatiguing Exercise 
Journal of Athletic Training  2006;41(1):79-86.
Context: Although poor paraspinal muscle endurance has been associated with less quadriceps activation (QA) in persons with a history of low back pain, no authors have addressed the acute neuromuscular response after lumbar paraspinal fatiguing exercise.
Objective: To compare QA after lumbar paraspinal fatiguing exercise in healthy individuals and those with a history of low back pain.
Design: A 2 × 4 repeated-measures, time-series design.
Setting: Exercise and Sport Injury Laboratory.
Patients or Other Participants: Sixteen volunteers participated (9 males, 7 females; 8 controls and 8 with a history of low back pain; age = 24.1 ± 3.1 years, height = 173.4 ± 7.1 cm, mass = 72.4 ± 12.1 kg).
Intervention(s): Subjects performed 3 sets of isometric lumbar paraspinal fatiguing muscle contractions. Exercise sets continued until the desired shift in lumbar paraspinal electromyographic median power frequency was observed. Baseline QA was compared with QA after each exercise set.
Main Outcome Measure(s): An electric burst was superimposed while subjects performed a maximal quadriceps contraction. We used the central activation ratio to calculate QA = (FMVIC/[FMVIC + FBurst])* 100, where F = force and MVIC = maximal voluntary isometric contractions. Quadriceps electromyographic activity was collected at the same time as QA measurements to permit calculation of median frequency during MVIC.
Results: Average QA decreased from baseline (87.4% ± 8.2%) after the first (84.5% ± 10.5%), second (81.4% ± 11.0%), and third (78.2% ± 12.7%) fatiguing exercise sets. On average, the group with a history of low back pain showed significantly more QA than controls. No significant change in quadriceps median frequency was noted during the quadriceps MVICs.
Conclusions: The quadriceps muscle group was inhibited after lumbar paraspinal fatiguing exercise in the absence of quadriceps fatigue. This effect may be different for people with a history of low back pain compared with healthy controls.
PMCID: PMC1421484  PMID: 16619099
superimposed burst technique; quadriceps muscle inhibition; low back pain
8.  Quadriceps Inhibition After Repetitive Lumbar Extension Exercise in Persons With a History of Low Back Pain 
Journal of Athletic Training  2006;41(3):264-269.
Context: A neuromuscular relationship exists between the lumbar extensor and quadriceps muscles during fatiguing exercise. However, this relationship may be different for persons with low back pain (LBP).
Objective: To compare quadriceps inhibition after isometric, fatiguing lumbar extension exercise between persons with a history of LBP and control subjects.
Design: A 2 × 3 factorial, repeated-measures, time-series design with independent variables of group (persons with a history of LBP, controls) and time (baseline, postexercise set 1, postexercise set 2).
Setting: University research laboratory.
Patients or Other Participants: Twenty-five subjects with a history of LBP were matched by sex, height, and mass to 25 healthy control subjects.
Intervention(s): Electromyography median frequency indexed lumbar paraspinal muscular fatigue while subjects performed 2 sets of isometric lumbar extension exercise. Subjects exercised until a 15% downward shift in median frequency for the first set and a 25% shift for the second set were demonstrated.
Main Outcome Measure(s): Knee extension force was measured while subjects performed an isometric maximal quadriceps contraction. During this maximal effort, a percutaneous electric stimulus was applied to the quadriceps, causing a transient, supramaximal increase in force output. We used the ratio between the 2 forces to estimate quadriceps inhibition. Quadriceps electromyographic activity was recorded during the maximal contractions to compare median frequencies over time.
Results: Both groups exhibited significantly increased quadriceps inhibition after the first (12.6% ± 10.0%, P < .001) and second (15.2% ± 9.7%, P < .001) exercise sets compared with baseline (9.6% ± 9.3%). However, quadriceps inhibition was not different between groups.
Conclusions: Persons with a history of LBP do not appear to be any more or less vulnerable to quadriceps inhibition after fatiguing lumbar extension exercise.
PMCID: PMC1569566  PMID: 17043693
superimposed burst technique; neuromuscular activity; knee
9.  A Functional Fatiguing Protocol and Deceleration Time of the Shoulder From an Internal Rotation Perturbation 
Journal of Athletic Training  2006;41(3):275-279.
Context: Muscular fatigue impedes sensorimotor function and may increase the risk of shoulder injury during activity. The effects of fatigue on the sensorimotor system of the shoulder have been studied with various results. Deceleration times have been used to study neuromuscular control of the shoulder; however, no studies involving the effects of fatigue on deceleration times have been reported.
Objective: To compare shoulder deceleration times after a shoulder internal rotation perturbation before and after a repetitive throwing exercise protocol.
Design: A 2 × 2 repeated-measures design.
Setting: Exercise and sport injury laboratory.
Patients or Other Participants: Twenty healthy, recreationally active men (age = 24.76 ± 4.03 years, height = 178.41 ± 8.36 cm, mass = 80.16 ± 15.20 kg) volunteered to participate in the study. To ensure familiarity with the overhead motion, all subjects chosen had previously participated in an overhead throwing sport.
Intervention(s): The independent variables were time (preintervention and postintervention) and session (experimental and control). The intervention consisted of continuous overhead throwing. The subjects were considered fatigued when a 10% decrease in velocity was noted on 3 consecutive pitches.
Main Outcome Measure(s): Time necessary to decelerate from an internal rotation perturbation.
Results: Deceleration time was significantly increased by the fatiguing intervention ( P = .001).
Conclusions: The decreased ability to decelerate may be an adaptive response by the subjects to dissipate a lower percentage of force per second.
PMCID: PMC1569554  PMID: 17043695
shoulder fatigue; shoulder neuromuscular control; throwing fatigue protocol
10.  Effects of Sport Massage on Limb Girth and Discomfort Associated With Eccentric Exercise 
Journal of Athletic Training  2005;40(3):181-185.
Context: Sport massage is often used to help prepare for exercise, expedite recovery from muscle soreness, and enhance athletic performance. However, the effect of sport massage on recovery from delayed-onset muscle soreness is unknown.
Objective: To determine the effect of a short sport massage treatment on intramuscular swelling and pain in response to eccentric exercise.
Design: We used a 2 × 8 (treatment × time) repeated-measures design to compare triceps surae muscle girth and pain ratings over the 72 hours after eccentric exercise.
Setting: University research laboratory.
Patients or Other Participants: Nineteen healthy, college-aged subjects.
Intervention(s): Delayed-onset muscle soreness was induced with several sets of eccentric triceps surae contractions at 90% of the estimated concentric, 1-repetition maximum weight. Subjects returned on 3 consecutive days after eccentric exercise with a cycle ergometer for active rest treatments. In addition, 1 leg received the sport massage.
Main Outcome Measure(s): Girth measurements were taken at 5.08 cm (2 in), 10.16 cm (4 in), 15.24 cm (6 in), and 20.32 cm (8 in) below the knee joint line, and pain was assessed with a visual analog scale before and after all 4 sessions.
Results: No interaction was noted between treatment and time for any girth or pain measurements, and no main effect was seen for treatment.
Conclusions: Sport massage did not reduce girth or pain in the lower leg after eccentric exercise within 72 hours.
PMCID: PMC1250257  PMID: 16284638
delayed-onset muscle soreness; active rest; rehabilitation; treatment
11.  Transcranial Magnetic Stimulation and Volitional Quadriceps Activation 
Journal of Athletic Training  2010;45(6):570-579.
Quadriceps-activation deficits have been reported after meniscectomy. Transcranial magnetic stimulation (TMS) in conjunction with maximal contractions affects quadriceps activation in patients after meniscectomy.
To determine the effect of single-pulsed TMS on quadriceps central activation ratio (CAR) in patients after meniscectomy.
Randomized controlled clinical trial.
University laboratory.
Patients or Other Participants:
Twenty participants who had partial meniscectomy and who had a CAR less than 85% were assigned randomly to the TMS group (7 men, 4 women; age  =  38.1 ± 16.2 years, height  =  176.8 ± 11.5 cm, mass  =  91.8 ± 27.5 kg, postoperative time  =  36.7 ± 34.9 weeks) or the control group (7 men, 2 women; age  =  38.2 ± 17.5 years, height  =  176.5 ± 7.9 cm, mass  =  86.2 ± 15.3 kg, postoperative time  =  36.6 ± 37.4 weeks).
Participants in the experimental group received TMS over the motor cortex that was contralateral to the involved leg and performed 3 maximal quadriceps contractions with the involved leg. The control group performed 3 maximal quadriceps contractions without the TMS.
Main Outcome Measure(s):
Quadriceps activation was assessed using the CAR, which was measured in 70° of knee flexion at baseline and at 0, 10, 30, and 60 minutes posttest. The CAR was expressed as a percentage of full activation.
Differences in CAR were detected over time (F4,72  =  3.025, P  = .02). No interaction (F4,72  =  1.457, P  =  .22) or between-groups differences (F1,18  =  0.096, P  =  .76) were found for CAR. Moderate CAR effect sizes were found at 10 (Cohen d  =  0.54, 95% confidence interval [CI]  =  −0.33, 1.37) and 60 (Cohen d  =  0.50, 95% CI  =  −0.37, 1.33) minutes in the TMS group compared with CAR at baseline. Strong effect sizes were found for CAR at 10 (Cohen d  =  0.82, 95% CI  =  −0.13, 1.7) and 60 (Cohen d  =  1.06, 95% CI  =  0.08, 1.95) minutes in the TMS group when comparing percentage change scores between groups.
No differences in CAR were found between groups at selected points within a 60-minute time frame, yet moderate to strong effect sizes for CAR were found at 10 and 60 minutes in the TMS group, indicating increased activation after TMS.
PMCID: PMC2978008  PMID: 21062180
central activation ratio; arthrogenic muscle inhibition; knee; meniscus
Quadriceps activation failure is common in patients with tibiofemoral osteoarthritis (TFOA) and has been reported to occur bilaterally following acute and chronic knee injuries. Sensory transcutaneous electrical stimulation (TENS) applied to the knee has increased ipsilateral quadriceps activation, yet it remains unknown if repeated sensory TENS treatments affect activation in the contralateral quadriceps.
To determine the effects of unilateral TENS treatment to the involved leg, in conjunction with 4-weeks of therapeutic exercise, on volitional quadriceps activation in the contralateral leg.
Thirty-three patients with radiographically diagnosed TFOA were randomly assigned to the TENS, placebo, and the control groups. The involved leg was defined as the knee with highest degree of radiographically assessed TFOA. All participants completed a supervised 4-week lower extremity exercise program for the involved leg only. TENS and placebo TENS were worn throughout the rehabilitation sessions as well as during daily activities for those groups on the involved leg. Quadriceps central activation ratio (CAR), a measure of volitional muscular activation, was assessed in the uninvolved leg at baseline, 2-weeks and 4-weeks following the initiation of the intervention.
There were no differences between groups for quadriceps CAR (P=0.3).
Although significant differences were not found, strong to moderate within group effect sizes were calculated for the TENS group at 2 (d = .87) and 4 weeks (d = .54), suggesting that significant differences may be found in a larger population.
Contralateral quadriceps CAR was not affected following a 4-week unilateral disinhibitory intervention in this sample.
PMCID: PMC2971644  PMID: 21589667
Voluntary activation; Arthrogenic muscle inhibition; Pain; Strength
13.  No Difference in Transverse Abdominis Activation Ratio between Healthy and Asymptomatic Low Back Pain Patients during Therapeutic Exercise 
Dysfunction of the transverse abdominis (TrA) has been associated with LBP. Several therapeutic exercises are prescribed to help target the TrA. Rehabilitative ultrasound imaging (RUSI) is used to capture activation of the TrA during exercise. The purpose was to examine TrA activation during the ADIM and quadruped exercises between healthy and nonsymptomatic LBP patients. We instructed the subjects how to perform the exercises and measured muscle thickness of the TrA at rest and during the exercises using RUSI. This allowed us to calculate TrA activation ratio during these exercises. We found no significant differences between activation ratios of the two groups during either exercise; however TrA activation during the ADIM was higher than the quadruped exercise. These exercises were capable of activating the TrA, which may be in part due to the verbal instruction they received. These exercises could be used during prevention or rehabilitation programs, since the TrA is activated.
PMCID: PMC3200274  PMID: 22110965
14.  Quadriceps Activation Following Knee Injuries: A Systematic Review 
Journal of Athletic Training  2010;45(1):87-97.
Arthrogenic muscle inhibition is an important underlying factor in persistent quadriceps muscle weakness after knee injury or surgery.
To determine the magnitude and prevalence of volitional quadriceps activation deficits after knee injury.
Data Sources:
Web of Science database.
Study Selection:
Eligible studies involved human participants and measured quadriceps activation using either twitch interpolation or burst superimposition on patients with knee injuries or surgeries such as anterior cruciate ligament deficiency (ACLd), anterior cruciate ligament reconstruction (ACLr), and anterior knee pain (AKP).
Data Extraction:
Means, measures of variability, and prevalence of quadriceps activation (QA) failure (<95%) were recorded for experiments involving ACLd (10), ACLr (5), and AKP (3).
Data Synthesis:
A total of 21 data sets from 18 studies were initially identified. Data from 3 studies (1 paper reporting data for both ACLd and ACLr, 1 on AKP, and the postarthroscopy paper) were excluded from the primary analyses because only graphical data were reported. Of the remaining 17 data sets (from 15 studies), weighted mean QA in 352 ACLd patients was 87.3% on the involved side, 89.1% on the uninvolved side, and 91% in control participants. The QA failure prevalence ranged from 0% to 100%. Weighted mean QA in 99 total ACLr patients was 89.2% on the involved side, 84% on the uninvolved side, and 98.5% for the control group, with prevalence ranging from 0% to 71%. Thirty-eight patients with AKP averaged 78.6% on the involved side and 77.7% on the contralateral side. Bilateral QA failure was commonly reported in patients.
Quadriceps activation failure is common in patients with ACLd, ACLr, and AKP and is often observed bilaterally.
PMCID: PMC2808760  PMID: 20064053
arthrogenic muscle inhibition; voluntary activation; twitch interpolation; superimposed burst; central activation ratio
15.  Jogging Kinematics After Lumbar Paraspinal Muscle Fatigue 
Journal of Athletic Training  2009;44(5):475-481.
Isolated lumbar paraspinal muscle fatigue causes lower extremity and postural control deficits.
To describe the change in body position during gait after fatiguing lumbar extension exercises in persons with recurrent episodes of low back pain compared with healthy controls.
Case-control study.
Motion analysis laboratory.
Patients or Other Participants:
Twenty-five recreationally active participants with a history of recurrent episodes of low back pain, matched by sex, height, and mass with 25 healthy controls.
We measured 3-dimensional lower extremity and trunk kinematics before and after fatiguing isometric lumbar paraspinal exercise.
Main Outcome Measure(s):
Measurements were taken while participants jogged on a custom-built treadmill surrounded by a 10-camera motion analysis system.
Group-by-time interactions were observed for lumbar lordosis and trunk angles (P < .05). A reduced lumbar spine extension angle was noted, reflecting a loss of lordosis and an increase in trunk flexion angle, indicating increased forward trunk lean, in healthy controls after fatiguing lumbar extension exercise. In contrast, persons with a history of recurrent low back pain exhibited a slight increase in spine extension, indicating a slightly more lordotic position of the lumbar spine, and a decrease in trunk flexion angles after fatiguing exercise. Regardless of group, participants experienced, on average, greater peak hip extension after lumbar paraspinal fatigue.
Small differences in response may represent a necessary adaptation used by persons with recurrent low back pain to preserve gait function by stabilizing the spine and preventing inappropriate trunk and lumbar spine positioning.
PMCID: PMC2742456  PMID: 19771285
gait analysis; spine
16.  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

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