Relationship of Physical Frailty to Phosphocreatine Recovery in Muscle after Mild Exercise Stress in the Oldest-Old Women

Background: Physical frailty is a clinical syndrome associated with aging and manifesting as slowness, weakness, reduced physical activity, weight loss, and/or exhaustion. Frail older adults often report that their major problem is “low energy”, and there is indirect evidence to support the hypothesis that frailty is a syndrome of dysregulated energetics. We hypothesized that altered cellular energy production underlies compromised response to stressors in the frail. Methods: We conducted a pilot study to assess muscle energetics in response to a mild isometric exercise challenge in women (n=30) ages 84–93 years. The frailty status was assessed by a validated physical frailty instrument. Localized phosphorus (P31) magnetic resonance spectroscopy with a 1.5T magnet was used to assess the kinetics of Phosphocreatine recovery in the tibialis anterior muscle following maximal isometric contraction for 30 seconds. Results: Phosphocreatine recovery following exertion, age-adjusted, was slowest in the frail group (mean=189 sec; 95%CI: 150,228) compared to pre-frail (mean=152 sec; 95%CI: 107,197) and nonfrail subjects (mean=132 sec; 95%CI: 40,224). The pre-frail and frail groups had 20 sec (95%CI: −49,89) and 57 sec (95%CI: −31,147) slower phosphocreatine recovery, respectively, than the non-frail. This response was paralleled by dysregulation in glucose recovery in response to oral glucose tolerance test in women from the same study population. Conclusions: Impaired muscle energetics and energy metabolism might be implicated in the physical frailty syndrome.