Intense interval training in healthy older adults increases skeletal muscle [(3)H]ouabain‐binding site content and elevates Na(+),K(+)‐ATPase α(2) isoform abundance in Type II fibers

Young adults typically adapt to intense exercise training with an increased skeletal muscle Na(+),K(+)‐ATPase (NKA) content, concomitant with reduced extracellular potassium concentration [K(+)] during exercise and enhanced exercise performance. Whether these changes with longitudinal training occur in older adults is unknown and was investigated here. Fifteen older adults (69.4 ± 3.5 years, mean ± SD) were randomized to either 12 weeks of intense interval training (4 × 4 min at 90–95% peak heart rate), 3 days/week (IIT, n = 8); or no exercise controls (n = 7). Before and after training, participants completed an incremental cycle ergometer exercise test until a rating of perceived exertion of 17 (very hard) on a 20‐point scale was attained, with measures of antecubital venous [K(+)](v). Participants underwent a resting muscle biopsy prior to and at 48–72 h following the final training session. After IIT, the peak exercise work rate (25%), oxygen uptake (16%) and heart rate (6%) were increased (P < 0.05). After IIT, the peak exercise plasma [K(+)](v) tended to rise (P = 0.07), while the rise in plasma [K(+)](v) relative to work performed (nmol.L(−1).J(−1)) was unchanged. Muscle NKA content increased by 11% after IIT (P < 0.05). Single fiber measurements, increased in NKA α(2) isoform in Type II fibers after IIT (30%, P < 0.05), with no changes to the other isoforms in single fibers or homogenate. Thus, intense exercise training in older adults induced an upregulation of muscle NKA, with a fiber‐specific increase in NKA α(2) abundance in Type II fibers, coincident with increased muscle NKA content and enhanced exercise performance.