Identifying clinically meaningful muscle power enhancements and their functional correlates in hospitalized older patients

Background This study aimed to determine the threshold of muscle power and strength enhancements that lead to functional gains after exercise intervention in an acute care unit. Methods A total of 302 older patients (intervention: 169, control: 133) from two randomized clinical trials were included (mean age 86.7 years). We measured maximal strength (1RM) and muscle power via a velocity transducer during leg press exercise at 30% and 60% of 1RM. A multicomponent exercise program, including power training, balance, and gait exercises performed over 3 to 6 consecutive days, served as the intervention. We used an anchor-based method to correlate muscle function increases with the Short Physical Performance Battery (SPPB) and gait velocity (GVT) to define clinically meaningful improvements (CMI). Results In the intervention group, marked differences were found in maximal power at 30% of 1RM between SPPB responders and non-responders (relative 83.5% vs. 34.8%; absolute 33.0 vs. 12.8 W; P<0.05) and at 60% of 1RM (relative 61.1% vs. 22.4%; P<0.05). GVT responders demonstrated significantly greater improvements in both relative and absolute maximal power than non-responders at both 30% and 60% of 1RM (P<0.05), as well as greater absolute 1RM gains (21.2 vs. 15.2 kg, P<0.05). CMI for muscle power based on SPPB and GVT ranged from 30.2% to 48.7%, whereas for 1RM, it was 8.2% based on GVT. Conclusion Muscle power gains were most notable in patients with improvements in the SPPB and GVT, highlighting the critical role of muscle power in functional recovery in these patients.