Everyday function in schizophrenia: The impact of aerobic endurance and skeletal muscle strength

Patients with schizophrenia suffer from physical health conditions, culminating in reduced physical functioning with enormous costs for patients and society. Although aerobic endurance and skeletal muscle strength, typically reduced in this population, relate to cognition and function, no study has explored their respective contributions to performance of functional skills and everyday tasks.

In a cross-sectional study, 48 outpatients (28/20 men/women; 35 ± 11(SD) years) with schizophrenia spectrum disorders (ICD-10; F20-25) were administered the UCSD Performance-based Skills Assessment-Brief (UPSA-B; functional skills), Specific Level of Functioning (SLOF; functional performance) and the Positive and Negative Syndrome (PANSS) scale. Peak oxygen uptake (V̇O_2peak) was assessed along with leg press maximal muscle strength (1RM) and mechanical power.

UPSA-B performance was associated with V̇O_2peak (r = 0.28,p < 0.05), accounting for 8 % (p < 0.05) of shared variance, but was unrelated to 1RM and mechanical power. The SLOF physical functioning domain was associated with V̇O_2peak (r = 0.30,p < 0.05) and 1RM (r = 0.24,p < 0.05), while SLOF personal care (r = 0.27,p < 0.05) and activities (r = 0.30,p < 0.05) were related only to V̇O_2peak. Hierarchical regression analyses revealed that while V̇O_2peak and age combined to account for 20 % (p < 0.05) of the variance in physical functioning, the contribution of 1RM was eliminated after adjusting for age. V̇O_2peak and negative symptoms combined predicted 24 % and 35 % of the variance in personal care and activities, respectively. UPSA-B scores did not add to the prediction of SLOF scores.

Although V̇O_2peak and 1RM both relate to functional outcomes, the combination of V̇O_2peak, age, and negative symptoms exert the greatest detrimental influence on functional performance beyond skills deficits.