Practice ameliorates deficits of isometric force production in +3 Gz

BACKGROUND: In our earlier work, we have shown that human subjects produce exaggerated isometric forces when exposed to three times terrestrial gravity (+3 Gz). In the present work, we investigated whether prolonged practice under +3 Gz reduces this deficit, and whether it affects the cognitive costs of force production.

METHODS: There were 24 young male student volunteers who produced forces without visual feedback of prescribed directions and magnitudes with their dominant hand, and used their other hand for a four-choice reaction-time task. Both tasks were performed separately and concurrently, in normal terrestrial gravity (normal G), 30 s after the beginning of +3 Gz, and after practice in +3 Gz.

RESULTS: During early +3 Gz responses, initial force (100 ms into the response) increased abruptly by about 140%, and peak-produced force by 30%. Both values decreased again after prolonged practice; this recovery was complete for peak force, but only partial for initial force. Dual-task interference was observed, which did not vary with G level or practice.

DISCUSSION: The detrimental effects of +3 Gz on force production are compensated for by adaptive reprogramming (see initial force) and by additional feedback-based corrections (see difference between peak and initial force). Force production is cognitively demanding, but cognitive costs do not seem to vary with G level or practice.