The influence of different floor stiffness on mechanical efficiency of leg extensor muscle

Abstract

The mechanical behaviour of skeletal muscle is influenced by internal factors (e.g. re-use of elastic energy) and/or external conditions (e.g. floor compliance, shoe structure etc.). These factors have an effect on muscular work economy-this was investigated in the present study. Eight subjects were tested during three different series of jumps. Each series consisted of rhythmical vertical jumps performed at desired frequency and height for 1 min. The first (1) series was executed on the laboratory floor without rebound condition (subjects were asked to maintain 1 s period in an isometric condition before concentric work was performed), the second (II) and the third (III) series were performed in rebound conditions respectively on a laboratory floor (hard surface) and on a special panel possessing high compliance (a special foam rubber panel with stiffness of 14.4 kN/m). Expired air was collected during the test and recovery for determination of energy expenditure. Mechanical work was calculated from the vertical displacement of the body during the jumps. The results indicated that the net efficiency in the jumps without prestretch of the leg extensor muscles (series I) was the lowest (19.4%). In contrast, the net efficiency observed in rebound jumps (series II and III) was respectively 30.8% and 33.1%, demonstrating that the reuse of elastic energy (Wel) plays an important role for muscular work efficiency. However, the contribution of Wel to the total work performed was different p < 0.05, Student's t-test) in jumps on the special panel (41%) compared to the normal surface (37%), even if the total amount of stored elastic energy was the same in both conditions. The different efficiency observed between series II and III was attributed to the compliance of the surface on which the tests were executed. It was suggested that man could change his neuromuscular pattern to adapt muscular behaviour for matching the damped properties shown by the high compliance surface. Finally, the soft surface may favour a very low rate of running injuries.

Effects of the transition time between muscle-tendon stretch and shortening on mechanical efficiency

“…The elastic energy restitution value of 43.7% obtained for series S 0 is lower than the results of Bosco et al (1997) who calculated an elastic energy restitution of 50% for vertical jumps. This small difference is normal because jumping involves much higher force values than the flexion-extension manoeuvre in the present paper.…”

Effects of different sport surfaces on muscle performance

“…The most important characteristic of a sport surface which may be related to performance seems to be its compliance. A person increases his leg stiffness (the stiffness of the integrated musculoskeletal system that behaves as a single linear spring during locomotion) when he is running or hopping on a compliant surface compared with running or hopping on a hard one [6,21,22,26,32,33]. Similarly, Daniel et al [13] have reported that runners adjust leg stiffness for their first step on a new running surface.…”

Aerobic-Anaerobic Profiles, Heart Rate and Match Analysis in Old Basketball Players

“…Before the test, players underwent a 10-min warm-up period (jogging and strolling locomotion at an exercise intensity of 40-60% VO 2max ). Five minutes after the end of the warm-up period, the anaerobic performances were measured indoors to avoid external interferences with the measurement system and to ensure that the compliance of the surface on which the tests were executed did not affect the jump scores [17] . The jump performances were evaluated by means of an optical acquisition system (Optojump, Microgate, Bolzano, Italy), developed to measure with 10 -3 s precision flight and ground contact times.…”