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Timothy F. Tyler, Brandon M. Schmitt, Stephen J. Nicholas, and Malachy P. McHugh


Hamstring-strain injuries have a high recurrence rate.


To determine if a protocol emphasizing eccentric strength training with the hamstrings in a lengthened position resulted in a low recurrence rate.


Longitudinal cohort study.


Sports-medicine physical therapy clinic.


Fifty athletes with hamstring-strain injury (age 36 ± 16 y; 30 men, 20 women; 3 G1, 43 G2, 4 G3; 25 recurrent injuries) followed a 3-phase rehabilitation protocol emphasizing eccentric strengthening with the hamstrings in a lengthened position.

Main Outcome Measures:

Injury recurrence; isometric hamstring strength at 80°, 60°, 40°, and 20° knee flexion in sitting with the thigh flexed to 40° above the horizontal and the seat back at 90° to the horizontal (strength tested before return to sport).


Four of the 50 athletes sustained reinjuries between 3 and 12 mo after return to sport (8% recurrence rate). The other 42 athletes had not sustained a reinjury at an average of 24 ± 12 mo after return to sport. Eight noncompliant athletes did not complete the rehabilitation and returned to sport before initiating eccentric strengthening in the lengthened state. All 4 reinjuries occurred in these noncompliant athletes. At time of return to sport, compliant athletes had full restoration of strength while noncompliant athletes had significant hamstring weakness, which was progressively worse at longer muscle lengths (compliance × side × angle P = .006; involved vs noninvolved at 20°, compliant 7% stronger, noncompliant 43% weaker).


Compliance with rehabilitation emphasizing eccentric strengthening with the hamstrings in a lengthened position resulted in no reinjuries.

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Gary E. Morin, David Tiberio, and Gary Austin

A characteristic of scapulothoracic dysfunction is the tendency for the upper regions of the trapezius to hypertrophy in relation to its middle and lower portions. This creates a muscular imbalance that can alter scapular position and subsequently the length–tension relationship of the shoulder muscles. Tape was applied over the right upper trapezius to inhibit electrical activity in the muscles of 10 uninjured subjects. EMG activity was recorded in two locations of the upper trapezius and one location in the middle to lower trapezius region while each subject maintained an isometric contraction designed to activate both muscles. With the tape applied, there was a statistically significant reduction in EMG activity of the upper trapezius with a corresponding increase in the middle/lower trapezius. The ability of the tape to alter trapezius activity in this fashion may help correct muscular imbalances in the trapezius muscle.

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Kurt Manal, Dustyn P. Roberts, and Thomas S. Buchanan

Ultrasonography was used to measure the pennation angle of the human tibialis anterior (TA), lateral gastrocnemius (LG), medial gastrocnemius (MG), and soleus (Sol). The right and left legs of 8 male and 8 female subjects were tested at rest and during maximum voluntary contraction (MVC). Joint angles were chosen to control muscle tendon lengths so that the muscles were near their optimal length within the length– tension relationship. No differences in pennation angle were detected between the right and left legs. Another consistent finding was that the pennation angle at MVC was significantly greater than at rest for all muscles tested. Optimal pennation angles for the TA, MG, and Sol were significantly greater for the men than for the women. Optimal pennation angles for the TA, LG, MG, and Sol for the male subjects were 14.3°, 23.7°, 34.6°, and 40.1° respectively, whereas values of 12.1°, 16.3°, 27.3°, and 26.3° were recorded for the female subjects. The results of this study suggest the following: (1) similar values for pennation angle can be used for the right and left TA, LG, MG, and Sol; (2) pennation angle is significantly greater at MVC than at rest for all muscles tested; and (3) sex-specific values for optimal pennation angle should be used when modeling the force-generating potential of the primary muscles responsible for ankle plantar and dorsiflexion.

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Xavier D. Thompson and Brianna DiAntonio

without damage, but if the length–tension relationship is altered and the optimum length for active tension is shortened, the risk of muscle damage is increased. 13 While this may have been attributable to the patient’s biceps femoris avulsion, sport-specific adaptations cannot be ruled out. 14 The

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Dae-Hyun Kim, Jin-Hee Lee, Seul-Min Yu, and Chang-Man An

muscle length–tension relationship. 13 The length–tension relationship is a biomechanical principle of variation in muscle tension due to muscle length changes. Skeletal muscles need more actin–myosin cross-bridges in order to produce higher magnitudes of force. However, if the sarcomere is not within

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Omid Kazemi, Amir Letafatkar, and Paulo H. Marchetti

production: the first one refers to mechanical factors, such as decreases in musculotendinous stiffness, which may affect the muscle’s length–tension relationship and sarcomere shortening velocity, and the second one refers to neural factors, such as decreases in muscle activation. 5 , 6 Fowles et al 8

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Nathan F. Johnson, Chloe Hutchinson, Kaitlyn Hargett, Kyle Kosik, and Phillip Gribble

and addressed in a clinical environment. A reduction in the extensibility of contractile and noncontractile soft tissue (ie, flexibility) decreases muscle performance and increases fall risk. 7 Muscle length–tension relationships are also important for optimal force generation. 8 Individuals with a

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Sajad Bagherian, Nader Rahnama, Erik A. Wikstrom, Micheal A. Clark, and Faroogh Rostami

hypothesis. Most compensations were eliminated when a heel lift was added. A heel lift is theorized to reduce knee valgus by increasing ankle plantar flexion and subsequently restoring the normal length-tension relationship of the lower leg musculature. 16 The heel lift is also hypothesized to shift the

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Félix Croteau, Shawn M. Robbins, and David Pearsall

length–tension relationships obtained in other angles. 7 The peak value was identified as the maximum value recorded within this filtered subset. Figure 2 Experimental setup for isokinetic strength testing. Participant in supine on the Contrex ™ device to measure isokinetic shoulder internal and

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Gareth Ryan, Heather Johnston, and Janice Moreside

length–tension relationship. Abduction elongates the infraspinatus, 27 which could have resulted in increased force production for a given activation level, and could account for the reduction in infraspinatus activation with abduction. Conversely, abduction shortens the posterior deltoid, which may