EFFECTS OF FATIGUE AND SPRINT TRAINING ON ELECTROMECHANICAL DELAY OF KNEE EXTENSOR MUSCLES

Electromechanical delay (EMD) of knee extensors in isometric contracti on was investigated in six healthy men before and after four periods o f 30-s all-out sprint cycling exercise, conducted pre and post a 7-wee k sprint cycling training programme. The EMD was lengthened from 40.4 (SEM 3.46) ms at rest to 63.4 (SEM 7.80) ms after the fatiguing exerci se (P less than or equal to 0.05) in the pre-training test. During max imal voluntary contractions (MVC) conducted after the fatiguing exerci se, the peak contraction force (F-peak) and peak rate of force develop ment (RFD(peak)) were reduced by 51%-56% and 38%-50%, respectively (bo th P less than or equal to 0.05). The mechanisms of EMD lengthening du ring fatigue could have been due to the deterioration in muscle conduc tive, contractile or elastic properties and require further study. The training programme increased the total work performed during the four periods of sprint exercise (P less than or equal to 0.05). However, n o significant training effects were found in the resting or postexerci se EMD, F-peak and RFD(peak) during isometric MVC. These unchanged iso metric contraction variables but enhanced dynamic performance suggest that isometric tests of muscle are insensitive to the neuromuscular ad aptations to sprint training.