Figure 3. Muscle sympathetic nerve activity burst frequencies for all astronauts in response to static handgrip.

Individual and mean (± s.e.m.) responses to static handgrip sustained to fatigue at 40 % of maximal voluntary contraction, followed by 2 min post-handgrip circulatory arrest pre-flight (n = 5), in-flight (n = 4) and post-flight (n = 5). Data were averaged for 1 min of baseline, 1 min of the initial static handgrip, the last 30 s of handgrip prior to fatigue (presented as ‘at fatigue’) and for each 1 min of post-handgrip circulatory arrest and recovery. The period between the end of the first minute and 30 s before fatigue was broken up into two equal periods and are depicted as ‘a’ and ‘b’ in the figure. BL, baseline; HG₁, first minute of static handgrip; HG_F, static handgrip at fatigue; C₁ and C₂, first and second minutes of post-handgrip circulatory arrest; R₁ and R₂, first and second minutes of recovery. * P < 0.05 and ** P < 0.01, compared with baseline; #P < 0.05, compared with pre-flight.