Practice ameliorates deficits of isometric force production in +3 Gz

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.

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.

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.

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.