Folland, J. P., & Fry, A. (2012). Neural drive during explosive force production exceeds that at maximum force. Presentation 2179 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

This investigation compared the magnitude and pattern of neural drive during explosive force production with neural drive registered in maximum voluntary force production in healthy, untrained, men (N = 27). Following familiarization, Ss performed two identical trials of isometric contractions of the knee extensors at a knee joint angle of 120°, seven days apart, with data averaged across both trials. Force was measured by a strain gauge perpendicular to the tibia and double differential surface EMG recorded from two sites over each of the three superficial quadriceps muscles (rectus femoris, vastus mdeialis, vastus lateralis). Ss performed: two series of four maximum voluntary contractions of three-seconds duration in order to measure maximum voluntary force and EMG amplitude; and 10 explosive contractions of ~one-second duration. For the explosive contractions, force was assessed for 200 ms after force onset, and EMG RMS amplitude measured in four successive 50-ms time periods after signal onset and the highest value from these time periods.

The maximally explosive EMG exceeded the maximal voluntary force EMG. This was also the case for all three individual muscles. Ss were divided into two groups according to relative explosive force after 100 ms (HIGH N = 14; LOW N = 13). The high group demonstrated a higher quadriceps EMG and this elevated neural drive was followed by a decline in EMG that was not the case for the low group. For individuals with high quadriceps EMG, this value was correlated with the subsequent decline in neural drive.

Implication. Neural drive during explosive force production was greater than in maximal voluntary contraction exercises, indicating that activation at maximum voluntary force in conventional exercises may be submaximal. Very high values of neural drive were associated with a subsequent decline indicating an inhibitory response. Greater stimulation is provided by explosive exercises than maximal conventional concentric contraction exercises. Explosive exercises might yield more appropriate stimulation for training speed and explosive actions.

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