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1.  Repeated Bout Effect Was More Expressed in Young Adult Males Than in Elderly Males and Boys 
BioMed Research International  2013;2013:218970.
This study investigated possible differences using the same stretch-shortening exercise (SSE) protocol on generally accepted monitoring markers (dependent variables: changes in creatine kinase, muscle soreness, and voluntary and electrically evoked torque) in males across three lifespan stages (childhood versus adulthood versus old age). The protocol consisted of 100 intermittent (30 s interval between jumps) drop jumps to determine the repeated bout effect (RBE) (first and second bouts performed at a 2-week interval). The results showed that indirect symptoms of exercise-induced muscle damage after SSE were more expressed in adult males than in boys and elderly males, suggesting that the muscles of boys and elderly males are more resistant to exercise-induced damage than those of adult males. RBE was more pronounced in adult males than in boys and elderly males, suggesting that the muscles of boys and elderly males are less adaptive to exercise-induced muscle damage than those of adult males.
PMCID: PMC3581300  PMID: 23484095
2.  Electromyographic Analysis of the Triceps Surae Muscle Complex During Achilles Tendon Rehabilitation Program Exercises 
Sports Health  2011;3(6):543-546.
Specific guidelines for therapeutic exercises following an Achilles tendon repair are lacking.
A hierarchical progression of triceps surae exercises can be determined on the basis of electromyographic (EMG) activity.
Study Design:
Randomized laboratory trial.
Bipolar surface electrodes were applied over the medial and lateral heads of the gastrocnemius as well as the soleus on 20 healthy lower extremities (10 participants, 27 ± 5 years old). Muscle activity was recorded during 8 therapeutic exercises commonly used following an Achilles repair. Maximal voluntary isometric contractions (MVICs) were also performed on an isokinetic device. The effect of exercise on EMG activity (% MVIC) was assessed using repeated measures analysis of variance with Bonferroni corrections for planned pairwise comparisons.
Seated toe raises (11% MVIC) had the least amount of activity compared with all other exercises (P < 0.01), followed by single-leg balance on wobble board (25% MVIC), prone ankle pumps (38% MVIC), supine plantarflexion with red elastic resistance (45% MVIC), normal gait (47% MVIC), lateral step-ups (60% MVIC), single-leg heel raises (112% MVIC), and single-leg jumping (129% MVIC).
There is an increasing progression of EMG activity for exercises that target the triceps surae muscle complex during common exercises prescribed in an Achilles tendon rehabilitation program. Seated toe raises offer relatively low EMG activity and can be utilized as an early rehabilitative exercise. In contrast, the single-leg heel raise and single-leg jumping should be utilized only during later-stage rehabilitation.
Clinical Relevance:
EMG activity in the triceps surae is variable with common rehab exercises.
PMCID: PMC3445221  PMID: 23016056
exercise prescription; gastrocnemius; soleus
Back ground and Purpose:
Hamstring injury is a common occurrence in sport and there has been limited success in reducing this rate of recurrence to date.
Description of Topic with Related Evidence:
High speed running requires eccentric strength when the hamstring muscles are in a lengthened state. The lengthened state occurs when the hip is in flexion and the lower leg moves into extension, thus lengthening the two joint hamstring muscle over both articulations upon which they act. There is evidence to suggest that athletes who have sustained a hamstring strain lack strength when the muscle is utilized during performance in a lengthened state.
To examine the risk factors contributing to such a high recurrence rate and propose a unique rehabilitation strategy addressing these factors in order to decrease the rate of reinjury.
Discussion/Relation to Clinical Practice:
Failing to increase an athlete's eccentric strength in a lengthened position after a hamstring injury may predispose an athlete to subsequent reinjury. Incorporating lengthened state eccentric training may help reduce the rate of reinjury.
Level of Evidence:
Level 5
PMCID: PMC3362981  PMID: 22666648
Hamstring strain; lengthened state eccentrics
4.  Shoulder Musculature Activity and Stabilization During Upper Extremity Weight-Bearing Activities 
Upper extremity weight-bearing exercises are routinely used in physical therapy for patients with shoulder pathology. However, little evidence exists regarding the demand on the shoulder musculature.
To examine changes in shoulder muscle activity and center of pressure during upper extremity weight-bearing exercises of increasing difficulty.
Electromyographic (EMG) and kinetic data were recorded from both shoulders of 15 healthy subjects (10 male and 5 female). Participants were tested in a modified tripod position under three conditions of increasing difficulty: (1) hand directly on the force plate, (2) on a green Stability Trainer™ and (3) on a blue Stability Trainer™. Ground reaction forces were recorded for each trial. Surface EMG was recorded from the serratus anterior, pectoralis major, upper trapezius, lower trapezius, infraspinatus, anterior deltoid, posterior deltoid, and the lateral head of the triceps muscles.
Mean deviation from center of pressure significantly increased when using the Stability Trainer™ pads. The activities of the triceps, serratus anterior, and anterior deltoid muscles significantly increased as each trial progressed, irrespective of stability condition. Additionally, activity in the anterior deltoid, lower trapezius, and serratus anterior muscles significantly decreased with increasing difficulty, whereas activity in the triceps muscles significantly increased.
Discussion and Conclusion
Balancing on a foam pad made it more difficult to maintain the upper extremity in a stable position. However, this activity did not alter the proprioceptive stimulus enough to elicit an increase in shoulder muscle activation. While the results on this study support the use of different level Stability Trainers™ to facilitate neuromuscular re-education, a less compliant unstable surface may produce larger training effects.
PMCID: PMC2953292  PMID: 21522206
closed chain; shoulder; muscle activity
5.  Surface Electromygraphic Analysis of the Lower Trapezius Muscle During Exercises Performed Below Ninety Degrees of Shoulder Elevation in Healthy Subjects 
The lower trapezius is an important muscle for normal arthrokinematics of the scapula. In the early stages of rehabilitation, it is generally accepted to perform exercises with the shoulder kept below 90° of elevation in order to minimize risk for shoulder impingement. Few exercises for the lower trapezius have been studied which maintain the shoulder below 90° of humeral elevation.
To identify therapeutic exercises performed below 90° of humeral elevation that activate marked levels of lower trapezius electromyographic (EMG) activity.
Surface EMG activity of the lower, middle, upper trapezius, and serratus anterior was collected bilaterally on fifteen healthy subjects during four exercises: the press-up, unilateral scapular retraction with the shoulder positioned at 80° of shoulder flexion, bilateral shoulder external rotation, and unilateral scapular depression.
The press-up exercise elicited marked lower trapezius EMG activity, moderate upper trapezius EMG activity, and a high ratio of lower trapezius to upper trapezius EMG activity. Scapular retraction produced marked EMG activity of both the lower and upper trapezius and moderate activity of the middle trapezius. Bilateral shoulder external rotation generated moderate lower trapezius EMG activity, minimal upper trapezius activity, and the highest ratio of lower trapezius to upper trapezius EMG activity. Scapular depression produced moderate lower trapezius EMG activity, mimimal upper trapezius EMG activity, and a moderately high ratio of lower trapezius to upper trapezius EMG activity.
Discussion and Conclusions
This study identified two exercises performed below 90° of humeral elevation that markedly activated the lower trapezius: the press-up and scapular retraction.
PMCID: PMC2953285  PMID: 21522201
lower trapezius; electromyography; scapula
6.  Electromyography of Selected Shoulder Musculature During Un-weighted and Weighted Pendulum Exercises 
Codman's pendulum exercises are commonly prescribed after shoulder surgery and injury to provide grade I and II distraction and oscillation resulting in decreased pain, increased flow of nutrients into the joint space, and early joint mobilization. Many shoulder protocols suggest that weight may be added to these pendulum exercises as rehabilitation progresses, however, very few guidelines exist to stipulate how much weight should be added.
To determine if added weight affected the subject's ability to relax the shoulder musculature during pendulum exercises.
Twenty-six participants, ages 20 to 56 years old (mean 32.26, ± 8.51 years) were divided into two groups, nine pathological and 17 non-pathological. The muscle activity (EMG) of four variations of Codman's pendulum exercises 1) wrist suspended 1.5 kg weighted-ball, 2) hand-held 1.5 kg dumbbell, 3) hand-held 1.5 kg weighted-ball, and 4) no weight were recorded in each muscle.
When grouped across all patients and all other factors included in the ANOVA, the type of pendulum exercise did not have a significant effect on shoulder EMG activity regardless of patient population or muscle tested. Generally, the supraspinatus/upper trapezius muscle activity was significantly higher than the deltoid and infraspinatus activity - especially in the patients with pathological shoulders
Performing the exercises with added weight did not result in significant increased shoulder EMG activity for the deltoid and infraspinatus muscles in subjects with and without shoulder pathology. However, patients with shoulder pathology had greater difficulty relaxing their supaspinatus/upper trapezius muscle group during Codman's pendulum exercises than healthy subjects.
PMCID: PMC2953311  PMID: 21522217
Codman; passive motion; distraction; muscle activity
7.  The Repeated Bout Effect: Does Evidence for a Crossover Effect Exist? 
Individuals undergoing an unaccustomed exercise bout incorporating a high degree of eccentric muscle contractions commonly experience delayed onset muscle soreness. The damage manifests itself via tenderness, loss of strength, swelling, elevated muscle enzyme activity and loss of flexibility. Following an initial "damage bout," a repeated bout results in reduced symptoms. This protective effect is known as the repeated bout effect (RBE) and can last up to 24 weeks between bouts. The mechanism for this RBE is unclear and both central and local mechanisms have been suggested. In an attempt to test the central hypothesis, 12 subjects (mean age = 22.5± 4yrs, ht = 167±9cm, mass = 71.5±13.5kg) underwent an exercise protocol whereby one leg was exercised eccentrically and following complete recovery; the contralateral leg was exercised in the same manner. Subjects were required to step on and off a 46-cm step for 20 minutes at a cadence of 15 steps/minute. One leg was used to go up the step (concentric) while the opposite was used to go down (eccentric). Approximately two weeks later and following complete recovery, the protocol was repeated with the concentrically exercise leg now performing the eccentric contraction. Data analyses indicate that muscle damage was induced during both trials on the eccentrically exercised leg as evidenced by a change in tenderness (bout 1 P < 0.05: bout 2 P < 0.01), pain scores (bout 1 P < 0.0001; bout 2 P < 0.01), and strength loss (bout 1 P = 0.001; bout 2 P = 0.001) over the four day follow up period. No tenderness was evident on the concentrically exercised limbs when compared to baseline (Bout 1: P =0.13, Bout 2: P = .06). Pain was significantly lower in bout two versus bout one (P< 0.04), however, we attribute this to a tolerance effect. Neither strength loss nor tenderness were significantly different between bouts. In the current study, damage was induced in both bouts in the eccentrically exercised limbs. This preliminary data does not provide evidence for a central mechanism in that an initial bout of eccentric exercise using one limb did not provide protection against damage from a repeated bout with the contralateral limb two weeks later.
PMCID: PMC3967433  PMID: 24701128
Eccentric; exercise; muscle damage; protection; contralateral
8.  Can exercise-induced muscle damage be avoided? 
Western Journal of Medicine  2000;172(4):265-266.
PMCID: PMC1070844  PMID: 10778382

Results 1-8 (8)