Electromechanical delay (EMD) and rate of force development (RFD) are determinants of explosive neuromuscular performance. We may expect a contrast in EMD and RFD between explosive power athletes, who have a demonstrable ability for explosive contractions, and untrained individuals. However, comparison and the neuromuscular mechanisms for any differences have not been studied.
The neuromuscular performance of explosive power athletes (n = 9) and untrained controls (n = 10) was assessed during a series of twitch, tetanic, explosive, and maximum voluntary isometric knee extensions. Knee extension force and EMG of the superficial quadriceps were measured in three 50-ms time windows from their onset and were normalized to strength and maximal M-wave (M max), respectively. Involuntary and voluntary EMD were determined from twitch and explosive voluntary contractions, respectively, and were similar for both groups.
The athletes were 28% stronger, and their absolute RFD in the first 50 ms was twofold that of controls. Athletes had greater normalized RFD (4.86 ± 1.46 vs 2.81 ± 1.20 MVC·s−1) and neural activation (mean quadriceps, 0.26 ± 0.07 vs 0.15 ± 0.06 M max) during the first 50 ms of explosive voluntary contractions. Surprisingly, the controls had a greater normalized RFD in the second 50 ms (6.68 ± 0.92 vs 7.93 ± 1.11 MVC·s−1) and a greater change in EMG preceding this period. However, there were no differences in the twitch response or normalized tetanic RFD between groups.
The differences in voluntary normalized RFD between athletes and controls were explained by agonist muscle neural activation and not by the similar intrinsic contractile properties of the groups.
1School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, UNITED KINGDOM; and 2Faculty of Sport, Pablo de Olavide University, Seville, SPAIN
Address for correspondence: Jonathan P. Folland, Ph.D., School of Sport andExercise Sciences, Loughborough University, Ashby Road, Loughborough, Leicestershire, LE11 3TU, United Kingdom; E-mail: J.P.Folland@lboro.ac.uk.
Submitted for publication December 2008.
Accepted for publication August 2009.