Follow-up of ankle stiffness and electromechanical delay in immobilized children: Three cases studies

Influence of simulated microgravity on mechanical properties in the human triceps surae muscle in vivo. I: effect of 120 days of bed-rest without physical training on human muscle musculo-tendinous stiffness and contractile properties in young women

Purpose

The aim of this study was to investigate the effect of a 120-day 5° head-down tilt (HDT) bed-rest on the mechanical properties of the human triceps surae muscle in healthy young women subjects.

Methods

Measurements included examination of the properties of maximal voluntary contractions (MVC), twitch contractions (P_t) and tetanic contractions (P_o). The difference between P_o and MVC expressed as a percentage of P_o and referred to as force deficiency (P_d), was calculated. Electromyographic (EMG) activity in the soleus muscle, electromechanical delay (EMD) and total reaction time (TRT) were also calculated. EMD was the time interval between the change in EMG and the onset of muscle tension. Premotor time (PMT) was taken to be the time interval from the delivery of the signal to change in EMG.

Results

After HDT P_t, MVC and P_o had decreased by 11.5, 36.1, 24.4 %, respectively, P_d had increased by 38.8 %. Time-to-peak tension had increased by 13.6 %, but half-relaxation time had decreased by 19.2 %. The rate of rise in isometric voluntary tension development had reduced, but no changes were observed in the electrically evoked contraction. EMD had increased by 27.4 %; PMT and TRT decreased by 21.4, and 13.7 %, respectively.

Conclusion

The experimental findings indicated that neural as well as muscle adaptation occurred in response to HDT. EMD is a simple and quick method for evaluation of muscle stiffness changes and can serve as an indicator of the functional condition of the neuromuscular system.

Effect of generalized joint hypermobility on knee function and muscle activation in children and adults

INTRODUCTION

We investigated muscle activation strategy and performance of knee extensor and flexor muscles in children and adults with generalized joint hypermobility (GJH) and compared them with controls.

METHODS

Muscle activation, torque steadiness, electromechanical delay, and muscle strength were evaluated in 39 children and 36 adults during isometric knee extension and flexion. Subjects performed isometric maximum contractions, submaximal contractions at 25% maximum voluntary contraction (MVC), and explosive contractions.

RESULTS

Agonist activation was reduced, and coactivation ratio was greater in GJH during knee flexion compared with controls. Torque steadiness was impaired in adults with GJH during knee flexion. No effect of GJH was found on muscle strength or electromechanical delay. Correlation analysis revealed an association between GJH severity and function in adults.

CONCLUSIONS

The results indicate that muscle activation strategy and quality of force control were significantly affected in adults with GJH during knee flexion, whereas only muscle activation strategy was affected in children with GJH.