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

Context:

Hamstring-strain injuries have a high recurrence rate.

Objective:

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

Design:

Longitudinal cohort study.

Setting:

Sports-medicine physical therapy clinic.

Participants:

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).

Results:

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).

Conclusion:

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

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Byron Lai, Eunbi Lee, Mayumi Wagatsuma, Georgia Frey, Heidi Stanish, Taeyou Jung and James H. Rimmer

youth periods provide health care professionals with an opportunity to promote health-enhancing physical activity behavior that can likely be sustained throughout the adult lifespan. Identifying effective physical activity approaches before and during this transitional period is critical, as the

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Shiu Hong Wong, Tianjian Ji, Youlian Hong, Siu Lun Fok and Lin Wang

The low impact forces of Tai Chi push-hand exercises may be particularly suited for older people and for those with arthritis; however, the biomechanics of push-hand exercises have not previously been reported. This paper examines the ground reaction forces (GRFs) and plantar force distributions during Tai Chi push-hand exercises in a stationary stance with and without an opponent. Ten male Tai Chi practitioners participated in the study. The GRFs of each foot were measured in three perpendicular directions using two force plates (Kistler). The plantar force distribution of each foot was measured concurrently using an insole sensor system (Novel). The results showed that the average maximum vertical GRF of each foot was not more than 88% ± 6.1% of the body weight and the sum of the vertical forces (103% ± 1.4%) generated by the two feet approximately equals the body weight at any one time. The horizontal GRFs generated by the two feet were in the opposite directions and the measured mean peak values were not more than 12% ± 2.8% and 17% ± 4.3% of the body weight in the medio-lateral and antero-posterior directions respectively. Among the nine plantar areas, the toes sustained the greatest plantar force. This study indicates that push-hand exercises generate lower vertical forces than those induced by walking, bouncing, jumping and Tai Chi gait, and that the greatest plantar force is located in the toe area, which may have an important application in balance training particularly for older adults.

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Gregory J. Steele, Rod A. Harter and Arthur J. Ting

The purpose of our study was to evaluate the functional outcomes of two methods of surgical treatment of acute closed raptures of the Achilles tendon, specifically, the primary open repair and the percutaneous repair techniques, utilizing (a) isokinetic plantar flexion strength, (b) midcalf girth, (c) ankle joint proprioception, and (d) ankle range of motion values. As a secondary purpose, the frequency of reruptures and postsurgical complications were compared between techniques. Twenty male patients (mean age, 43.8 ± 9.4 years) who sustained complete, closed ruptures of the Achilles tendon participated in this study. Results of paired t tests revealed significant differences between postsurgical and contralateral normal limbs for 6 of 12 variables. Results of the ANOVAs revealed no significant differences between the open repair group and percutaneous repair group for any of the evaluative parameters. The significant deficits in postoperative isokinetic plantar flexion strength and midcalf girth measurements, irrespective of surgical technique, suggest an incompleteness of rehabilitation or, more likely, the physiological inability to regain these characteristics postoperatively.

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Anthony S. Kulas, Thomas C. Windley and Randy J. Schmitz

Context:

Functional implications of clinically relevant abdominal postures have been sparsely examined.

Objectives:

To evaluate the reliability of sustaining abdominal postures during single-leg landings and the effects of abdominal postures on lower extremity kinetics and energetics.

Design:

One-way ANOVA tested effects of leg-spring stiffness and lower extremity energetics across groups (control, abdominal hollowing [AH], and pelvic tilting [PT]).

Participants:

12 male (24.0 ± 3.4 years) and 12 female (21.9 ± 2.3 years) healthy, recreationally active subjects.

Main Outcome Measures:

Leg-spring stiffness and relative joint-energy absorption from control, AH, and PT groups.

Results:

AH and PT ICCs2,k and standard error of measurements (AH = 0.53 ± 0.4 cm, PT = 0.9° ± 0.8°) were moderate to high. Relative knee-energy-absorption effect sizes comparing the control and treatment groups revealed moderate treatment effects (AH = 0.66%, PT = 0.41%).

Conclusions:

Abdominal postures can be reliably performed during a single-leg-landing task. Energy-absorption effect sizes suggest a link between the trunk and lower extremity.

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Viviane Kostrubiec, Régis Soppelsa, Jean-Michel Albaret and Pier-Giorgio Zanone

This study investigates how motor coordination undergoes the passage from a discrete to a continuous movement régime. Participants repeated concatenated discrete movements with each hand such that one hand was lagging the other by a quarter of a cycle (i.e., with a 90° phase difference). As movement frequency increased, the tendency to persist in this relative phase competed with a progressive effect of the interlimb coupling favoring 0° and 180°. In 61% of the participants, a switch from a discrete to a continuous motion régime was accompanied by a shift toward the 0° or 180°. The 0° was more often favored than 180°. The remaining participants sustained a relative phase close to 90° even at the highest movement frequency and proved to be more accurate at the initial lowest frequency. These findings indicate that a priming effect may circumvent the tendency to produce preferred patterns and favor the production of nonpreferred patterns and that initial individual differences affect how motor coordination evolves with changing constraints.

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David E. Krebs, Peter H. Velyvis and Mark W. Rogers

This study examined the prevalence of protective stepping and accompanying preparatory postural responses associated with lateral weight transfer (WT) while subjects attempted to sustain stationary standing. The subjects were 92 healthy young and older adults and persons with vestibular hypo-function. Force platform and whole-body-motion recordings were used to evaluate the prevalence of stepping and WT responses during stationary standing (eyes open or closed) using a semi-tandem foot position. WT components were also evaluated for volitionally requested step initiation, and as a function of support base configuration and direction of stepping among younger subjects. Only 10% of trials by subjects with bilateral vestibular hypofunction (BVH) during semi-tandem standing with eyes closed were completed without a step, while 31% of subjects with UVH, 69% of healthy elders, and all young healthy subjects were able to stand for the entire 7-sec trials. WT responses always preceded volitional steps from a standard feet-parallel orientation but occurred in only 13% of the spontaneous steps. The prevalence of WT was influenced by the direction of volitional stepping from semi-tandem standing, but not by the initial standing width. Spontaneous stepping to maintain standing balance is a naturally occurring and prevalent behavior among older adults and persons with vestibular hypo-function during tests of quasi-static standing. Differences between volitional and spontaneous step initiation involving the prevalence of preparatory lateral WT are a complex function of motor planning, mechanical constraints, and functional context.

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Alison C. McDonald, Elora C. Brenneman, Alan C. Cudlip and Clark R. Dickerson

As the modern workplace is dominated by submaximal repetitive tasks, knowledge of the effect of task location is important to ensure workers are unexposed to potentially injurious demands imposed by repetitive work in awkward or sustained postures. The purpose of this investigation was to develop a three-dimensional spatial map of the muscle activity for the right upper extremity during laterally directed submaximal force exertions. Electromyographic (EMG) activity was recorded from fourteen muscles surrounding the shoulder complex as the participants exerted 40N of force in two directions (leftward, rightward) at 70 defined locations. Hand position in both push directions strongly influenced total and certain individual muscle demands as identified by repeated measures analysis of variance (P < .001). During rightward exertions individual muscle activation varied from 1 to 21% MVE and during leftward exertions it varied from 1 to 27% MVE with hand location. Continuous prediction equations for muscular demands based on three-dimensional spatial parameters were created with explained variance ranging from 25 to 73%. The study provides novel information for evaluating existing and proactive workplace designs, and may help identify preferred geometric placements of lateral exertions in occupational settings to lower muscular demands, potentially mitigating fatigue and associated musculoskeletal risks.

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Cheng-Feng Lin, Hui Liu, William E. Garrett and Bing Yu

Small knee flexion angle during landing has been proposed as a potential risk factor for sustaining noncontact ACL injury. A brace that promotes increased knee flexion and decreased posterior ground reaction force during landing may prove to be advantageous for developing prevention strategies. Forty male and forty female recreational athletes were recruited. Three-dimensional videographic and ground reaction force data in a stop-jump task were collected in three conditions. Knee flexion angle at peak posterior ground reaction force, peak posterior ground reaction force, the horizontal velocity of approach run, the vertical velocity at takeoff, and the knee flexion angle at takeoff were compared among conditions: knee extension constraint brace, nonconstraint brace, and no brace. The knee extension constraint brace significantly increased knee flexion angle at peak posterior ground reaction force. Both knee extension constraint brace and nonconstraint brace significantly decreased peak posterior ground reaction force during landing. The brace and knee extension constraint did not significantly affect the horizontal velocity of approach run, the vertical velocity at takeoff, and the knee flexion angle at takeoff. A knee extension constraint brace exhibits the ability to modify the knee flexion angle at peak posterior ground reaction force and peak posterior ground reaction force during landing.

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Gregory M. Gutierrez, Nicole D. Jackson, Kristin A. Dorr, Sarah E. Margiotta and Thomas W. Kaminski

Context:

Lateral ankle sprains occur more frequently than any other orthopedic injury. Athletes often report sustaining more injuries late in competition when fatigue is present.

Objective:

To evaluate neuromuscular function of the ankle musculature after fatigue. Design: Experimental, pretest-posttest.

Setting:

Research laboratory.

Participants:

Ten female and 9 male college-aged subjects.

Intervention:

Fatigue was induced via continuous concentric and eccentric muscle actions of the ankle: inversion (INV), eversion (EV), plantar flexion (PF), and dorsiflexion (DF).

Main Outcome Measures:

Peak torque (PT), peak EMG, and median frequency (MF) were calculated prefatigue and postfatigue in the tibialis anterior (TA), peroneus longus (PER), and lateral gastrocnemius (GAS) muscles.

Results:

Main effects were noted for test (P < 0.0125) in all statistical tests performed indicating changes in PT, peak EMG, and MF after fatigue.

Conclusions:

A significant decrease in MF of the PER muscle after PF fatigue and corresponding with a decreased firing rate, may be of importance, especially with regard to the role in countering the violent moment seen with inversion ankle sprains.