Differences in force gradation between tug-of-war athletes and non-athletes during rhythmic force tracking at high exertion levels.

There is little knowledge regarding the force production capacities of tug-of-war athletes, who undergo years of high-load strength training on handgrip muscles. The purpose of this investigation was to determine the force-grading strategies of tug-of-war athletes by examining force fluctuation properties at high exertion levels. Sixteen tug-of-war athletes and sixteen sedentary non-athletes performed sinusoidal handgrip grip at 50%-100% of maximal effort at 0.5 Hz under visual guidance. Force outputs of the designate task were recorded with a strain gauge. Force fluctuations were separated from the rhythmic output of the target rate in the handgrip force. In addition to a comparable normalized tracking error, the tug-of-war athletes exhibited a greater mean force output (Fmean) and a higher ratio of mean force output (Fmean) to body mass than the non-athletes. The athletes also had lower approximate entropy (ApEn) and a lower mean frequency of force fluctuations than the non-athletes, despite a similar relative size of force fluctuations for the two groups. The scaling of the fundamental element (force pulses) of force fluctuations was also group-dependent, with a greater pulse gain (duration-amplitude regression slope) than the non-athletes. The tug-of-war athletes exhibited superior force-generating capacity and more economic force-grading as compared with the non-athletes, without additional costs to task accuracy and force steadiness, during a highly-demanding rhythmic force task.