Delayed influence of stretch-shortening cycle fatigue on large ankle joint position coded with static positional signals

Neuro-mechanical adjustments to shod versus barefoot treadmill runs in the acute and delayed stretch-shortening cycle recovery phases

In habitually shod recreational runners, we studied the combined influence of footwear and stretch-shortening cycle (SSC) fatigue on treadmill running pattern, paying special attention to neuro-mechanical adjustments in the acute and 2-day delayed recovery periods. The SSC exercise consisted of a series of 25 sub-maximal rebounds on a sledge apparatus repeated until exhaustion. The acute and delayed functional fatigue effects were quantified in a maximal drop jump test. The neuro-mechanical adjustments to fatigue were examined during two submaximal treadmill run tests of 3 min performed either barefoot or with shoes on. Surface electromyographic (EMG) activities, tibial accelerations and kinematics of the right lower limb were recorded during the first and last 15 s of each run. The main result was that neuro-mechanical differences between the shod and barefoot running patterns, classically reported in the absence of fatigue, persisted in the fatigued state. However, in the delayed recovery phase, rearfoot eversion was found to significantly increase in the shod condition. This specific footwear effect is considered as a potential risk factor of overuse injuries in longer runs. Therefore, specific care should be addressed in the delayed recovery phase of SSC fatigue and the use of motion control shoes could be of interest.

Altered force ratio in unanticipated side jumps after treadmill run

OBJECTIVE

The aim was to investigate the influence of a run at the individual anaerobic threshold (IAT) on postural control in jumps with an unanticipated change of direction.

HYPOTHESIS

Dynamic postural control is less affected by the run in trained athletes than in recreational ones.

DESIGN

: Controlled prospective cohort study with an intervention.

SETTING

Biomechanics laboratory.

PARTICIPANTS

A total of 18 female high-level handball and volleyball players, 16 female and 8 male recreational athletes, with a mean age of 21.7 +/-4.1 years.

INTERVENTIONS

In the jump test, the ball switch, hit above the force plate during a forward jump, triggers indicator lamps on either side. After landing on the dominant leg, a second jump 90 degrees sideways following a light signal or a stabilization in one-leg stance was required. Nine jumps (randomized order) were performed before and at 1, 5, 10, 15 and 20 min after a 30-min treadmill run at the IAT.

MAIN OUTCOME MEASUREMENTS

For the second jump, the ratio of the absolute values of the maximum forces in anteroposterior and mediolateral direction was calculated as a parameter of dynamic postural control in the change of direction.

RESULTS

In both groups, the force ratio increased significantly at 1 and 5 min after the treadmill run. The relative increase did not differ between groups. Dynamic postural control in transfer from a forward to a sideward jump was reduced after the run. Recovery occurred within 10 min.

CONCLUSIONS

This study shows that dynamic postural control in jumps with an unanticipated change of direction is influenced by fatigue. These findings could be used to develop training programs aimed at reducing lower limb injuries in high-level ball sport athletes. The preventive effects have to be evaluated in further studies.