Oxygen uptake kinetics measured at the onset of comfortable self-paced walking in elderly women after hip fracture

The objectives of this study were to (1) evaluate the suitability of “comfortable” self-paced walking as a mode of exercise to study VO₂ kinetics, and (2) to investigate VO₂ kinetics after hip fracture using self-paced walking as the exercise mode. The study took place in a Scottish rehabilitation hospital physiotherapy gymnasium [hip fracture (HF) group] and a Scottish University Gymnasium [young (Y) and healthy elderly (HE) groups]. Fifteen women after HF (median age 81 years) and five Y and five older HE women (median ages 22 and 78 years, respectively) took part in the study. Volunteers completed three repeats of 3 min of “comfortable” self-paced walking on two occasions. The ensemble averaged VO₂ response from walks 2 and 3 on visits 1 and 2 were combined and characterised using nonlinear regression techniques to derive a Mean Response Time (MRT). Self-paced walking was described as “constant-load” exercise (coefficient of variation of lap speeds of ≤6%) in 13 of 15 cases in the HF group on at least one visit (100% of cases in Y and HE groups). Steady-state VO₂ was achieved in 3 min in 8 of HF group on Visit 1 and 10 on Visit 2 (100% of cases in Y and HE groups). MRTs for the HF group (51 s, N = 5, 4 repeats; N = 7, 2 repeats) were significantly higher than the Y and HE groups [Y group 22 s (N = 5, 4 repeats); HE group 36 s (N = 5, 4 repeats)]. Self-paced walking provided a suitable mode of exercise to investigate VO₂ kinetics in frail older women after HF and permitted the first characterisation of VO₂ kinetics in this patient group. This test provides a promising methodology to evaluate rehabilitation efforts in frail individuals.