Load knowledge reduces rapid force production and muscle activation during maximal-effort concentric lifts

Rapid force development is a key factor influencing performance and injury risk in movements where little time is available for force production; thus there is a need to develop interventions that enhance this ability. In the present study, the influence of load knowledge on mechanical output [rate of force development; (RFD) and power] and muscle activation [electromyographic (EMG) responses] in the concentric-only bench press throw exercise was studied.

Fifteen strength-trained individuals performed 6 sets of 6 maximal explosive repetitions in a single test session after extensive familiarization. In three of these sets the subjects were given knowledge about the load before each repetition (known condition; KC), whereas in the other three sets they were given no information (unknown condition; UC). In both conditions the loads were 30, 50 and 70 % of maximum, but condition and load orders were randomized.

RFD (24-50 %) and power output (20-39 %) were significantly higher in UC in the early time intervals from movement onset (<150 ms). In addition, UC elicited greater EMG amplitudes in anterior deltoid both prior to movement onset (pre50-0 ms) and in the early time intervals (<100 ms) after movement onset, and in pectoralis major after movement onset (<100 ms).

UC resulted in a greater initial activation of the muscles and both a higher RFD and mechanical power output in the early phase of the movement under all loading conditions (30-70 % of maximum). UC appears to offer a novel neuromuscular stimulus, and further research on the effects of continued exposure is warranted.