The effects of high altitude (3,800 m) on postactivation potentiation in females and males

We investigated the effects of high altitude (HA) on postactivation potentiation (PAP) of the quadriceps muscles in 18 healthy adults (10 females). At sea level (SL; 300 m), and again after 1–2 and 11–13 days of residing at 3,800 m (HA1 and HA2, respectively), single electrical stimuli were delivered to the femoral nerve to quantify parameters of the resting twitch and the maximal compound muscle action potential (M_max), before and 2–300 s after a 10-s maximal voluntary contraction (i.e., the conditioning contraction). PAP was quantified by comparing peak force of twitches evoked after the conditioning contraction to the control twitch before it. On all days of testing, twitches were potentiated from 2 to 180 s (P ≤ 0.003). At SL, PAP was greater for males than females 2 and 15 s after the conditioning contraction (by 29.6% and 17.5%, respectively; P ≤ 0.005). For males, PAP was ~19% lower at HA1 than SL (P ≤ 0.001), a deficit that persisted at HA2 (P = 0.001). Conversely, the magnitude of PAP did not change with HA for females (P ≥ 0.808). Finally, the M_max amplitude was greater at HA1 and HA2 compared with SL (P ≤ 0.039), with no difference between the sexes. From our findings, it can be suggested that mechanisms related to PAP of the quadriceps muscles are affected by HA (3,800 m) in healthy adult males but not females.