Progressive Strength Training Counteracts Frailty but Does not Improve Short-Term Autonomic Compensatory Responses During Active Standing Orthostatic Stress

Background. Frailty is a multifactorial condition that significantly impacts older adults' health and independence, which can be mitigated through training. This study examined the effects of a 12-week progressive strength training (PST) program on frailty status and short-term autonomic compensatory responses during postural transitions. Methods: Eight older adults (60-79 years) classified as pre-frail or frail according to the frailty index (FI) participated in a 12-week PST program. Time and frequency-domain heart rate varia-bility (HRV) in the supine position, cardiac parasympathetic modulation (CPM) deter-mined from the HR 30:15 ratio (longest RR interval around the 30th heartbeat divided by the shortest RR interval around the 15th heartbeat after standing), and cardiac baroreceptor gain (CBG) assessed as the ratio of heart rate change to systolic blood pressure drop (ΔHR/ΔSBP) at 30, 60, 180, and 420 seconds after standing were assessed at pre-test, 8 weeks and 12 weeks (autonomic function outcomes). The level of physical activity (LPA), handgrip strength (HGS), and gait speed (GS) were assessed, and orthostatic intolerance (OI) symptoms were self-reported at pre-test, 8 weeks and 12 weeks. Results: After 12 weeks of PST, FI scores decreased from 0.18 to 0.04 (78% reduction). LPA, HGS, and GS improved by 152%, 13%, and 11%, respectively. Three of eight participants reported OI symptoms at pre-test, with no reported symptoms at week 12. Despite this, PST did not enhance short-term autonomic responses. Conclusion: PST counteracted frailty and im-proved physical and muscular function but did not enhance indices of short-term auto-nomic regulation in frail older people.