Copers and Noncopers Use Different Landing Techniques to Limit Anterior Tibial Translation After Anterior Cruciate Ligament Reconstruction.

BACKGROUND: At 1 year after anterior cruciate ligament reconstruction (ACLR), two-thirds of patients manage to return to sports (copers), whereas one-third of patients do not return to sports (noncopers). Copers and noncopers have different muscle activation patterns, and noncopers may not be able to control dynamic anterior tibial translation (ATTd) as well as copers. PURPOSE/HYPOTHESIS: To investigate whether (1) there is a positive correlation between passive ATT (ATTp; ie, general joint laxity) and ATTd during jump landing, (2) whether ATTd is moderated by muscle activating patterns, and (3) whether there is a difference in moderating ATTd between copers and noncopers. We hypothesized that patients who have undergone ACLR compensate for ATTd by developing muscle strategies that are more effective in copers compared with noncopers. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 40 patients who underwent unilateral ACLR performed 10 single-leg hops for distance with both legs. Lower body kinematic and kinetic data were measured using a motion-capture system, and ATTd was determined with an embedded method. Muscle activity was measured using electromyographic signals. Bilateral ATTp was measured using a KT-1000 arthrometer. In addition, the Beighton score was obtained. RESULTS: There was no significant correlation between ATTp and ATTd in copers; however, there was a positive correlation between ATTp and ATTd in the operated knee of noncopers. There was a positive correlation between the Beighton score and ATTp as well as between the Beighton score and ATTd in both copers and noncopers in the operated knee. Copers showed a negative correlation between ATTd and gastrocnemius activity in their operated leg during landing. Noncopers showed a positive correlation between ATTd and knee flexion moment in their operated knee during landing. CONCLUSION: Copers used increased gastrocnemius activity to reduce ATTd, whereas noncopers moderated ATTd by generating a smaller knee flexion moment. CLINICAL RELEVANCE: This study showed that copers used different landing techniques than noncopers. Patients who returned to sports after ACLR had sufficient plantar flexor activation to limit ATTd.

Power Training-induced Increases in Muscle Activation during Gait in Old Adults.

INTRODUCTION/PURPOSE: Aging modifies neuromuscular activation of agonist and antagonist muscles during walking. Power training can evoke adaptations in neuromuscular activation that underlie gains in muscle strength and power but it is unknown if these adaptations transfer to dynamic tasks such as walking. We examined the effects of lower-extremity power training on neuromuscular activation during level gait in old adults. METHODS: Twelve community-dwelling old adults (age ≥ 65 yr) completed a 10-wk lower-extremity power training program and 13 old adults completed a 10-wk control period. Before and after the interventions, we measured maximal isometric muscle strength and electromyographic (EMG) activation of the right knee flexor, knee extensor, and plantarflexor muscles on a dynamometer and we measured EMG amplitudes, activation onsets and offsets, and activation duration of the knee flexors, knee extensors, and plantarflexors during gait at habitual, fast, and standardized (1.25 ± 0.6 m·s) speeds. RESULTS: Power training-induced increases in EMG amplitude (~41%; 0.47 ≤ d ≤ 1.47; P ≤ 0.05) explained 33% (P = 0.049) of increases in isometric muscle strength (~43%; 0.34 ≤ d ≤ 0.80; P ≤ 0.05). Power training-induced gains in plantarflexor activation during push-off (+11%; d = 0.38; P = 0.045) explained 57% (P = 0.004) of the gains in fast gait velocity (+4%; d = 0.31; P = 0.059). Furthermore, power training increased knee extensor activation (~18%; 0.26 ≤ d ≤ 0.29; P ≤ 0.05) and knee extensor coactivation during the main knee flexor burst (~24%, 0.26 ≤ d ≤ 0.44; P ≤ 0.05) at habitual and fast speed but these adaptations did not correlate with changes in gait velocity. CONCLUSIONS: Power training increased neuromuscular activation during isometric contractions and level gait in old adults. The power training-induced neuromuscular adaptations were associated with increases in isometric muscle strength and partly with increases in fast gait velocity.

Hip mechanics underlie lower extremity power training-induced increase in old adults' fast gait velocity: The Potsdam Gait Study (POGS).

BACKGROUND: Aging is associated with slowed gait and old compared with young adults generally walk with greater positive hip work (H1) and reduced positive ankle work (A2). The role of exercise interventions on old adults' gait mechanics that underlie training-induced improvements in gait velocity is unclear. We examined the effects of lower extremity power training and detraining on old adults' gait kinetics. METHODS: As part of the Potsdam Gait Study (POGS), healthy old adults completed a no-intervention control period (69.1±4.4yrs, n=14) or a power training program followed by detraining (72.9±5.4yrs, n=15). We measured isokinetic knee extensor and plantarflexor power and measured hip, knee and ankle kinetics at habitual, fast and standardized walking speeds. RESULTS: Power training significantly increased isokinetic knee extensor power (25%), plantarflexor power (43%), and fast gait velocity (5.9%). Gait mechanics underlying the improved fast gait velocity included increases in hip angular impulse (29%) and H1 work (37%) and no changes in positive knee (K2) and A2 work. Detraining further improved fast gait velocity (4.7%) with reductions in H1 (-35%), and increases in K2 (36%) and A2 (7%). CONCLUSION: Power training increased fast gait velocity in healthy old adults by increasing the reliance on hip muscle function and thus further strengthened the age-related distal-to-proximal shift in muscle function.

Kinematic Mechanisms of How Power Training Improves Healthy Old Adults' Gait Velocity.

INTRODUCTION: Slow gait predicts many adverse clinical outcomes in old adults, but the mechanisms of how power training can minimize the age-related loss of gait velocity is unclear. We examined the effects of 10 wk of lower extremity power training and detraining on healthy old adults' lower extremity muscle power and gait kinematics. METHODS: As part of the Potsdam Gait Study, participants started with 10 wk of power training followed by 10 wk of detraining (n = 16), and participants started with a 10-wk control period followed by 10 wk of power training (n = 16). We measured gait kinematics (stride characteristic and joint kinematics) and isokinetic power of the ankle plantarflexor (20°·s, 40°·s, and 60°·s) and knee extensor and flexor (60°·s, 120°·s, and 180°·s) muscles at weeks 0, 10, and 20. RESULTS: Power training improved isokinetic muscle power by ~30% (P ≤ 0.001) and fast (5.9%, P < 0.05) but not habitual gait velocity. Ankle plantarflexor velocity measured during gait at fast pace decreased by 7.9% (P < 0.05). The changes isokinetic muscle power and joint kinematics did not correlate with increases in fast gait velocity. The mechanisms that increased fast gait velocity involved higher cadence (r = 0.86, P ≤ 0.001) rather than longer strides (r = 0.49, P = 0.066). Detraining did not reverse the training-induced increases in muscle power and fast gait velocity. CONCLUSION: Because increases in muscle power and modifications in joint kinematics did not correlate with increases in fast gait velocity, kinematic mechanisms seem to play a minor role in improving healthy old adults' fast gait velocity after power training.

Effects of Power Training on Mobility and Gait Biomechanics in Old Adults with Moderate Mobility Disability: Protocol and Design of the Potsdam Gait Study (POGS).

BACKGROUND: Walking speed decreases in old age. Even though old adults regularly participate in exercise interventions, we do not know how the intervention-induced changes in physical abilities produce faster walking. The Potsdam Gait Study (POGS) will examine the effects of 10 weeks of power training and detraining on leg muscle power and, for the first time, on complete gait biomechanics, including joint kinematics, kinetics, and muscle activation in old adults with moderate mobility disability. METHODS/DESIGN: POGS is a randomized controlled trial with two arms, each crossed over, without blinding. Arm 1 starts with a 10-week control period to assess the reliability of the tests and is then crossed over to complete 25-30 training sessions over 10 weeks. Arm 2 completes 25-30 exercise sessions over 10 weeks, followed by a 10-week follow-up (detraining) period. The exercise program is designed to improve lower extremity muscle power. Main outcome measures are: muscle power, gait speed, and gait biomechanics measured at baseline and after 10 weeks of training and 10 weeks of detraining. DISCUSSION: It is expected that power training will increase leg muscle power measured by the weight lifted and by dynamometry, and these increased abilities become expressed in joint powers measured during gait. Such favorably modified powers will underlie the increase in step length, leading ultimately to a faster walking speed. POGS will increase our basic understanding of the biomechanical mechanisms of how power training improves gait speed in old adults with moderate levels of mobility disabilities.