Comparison of neural activation and energy cost during treadmill walking with body weight unloading between frail and healthy older women

The aims of the study were to investigate whether body weight unloading (BWU) enables frail older women to walk on a treadmill without increasing energy and cardiac cost compared to normal gravity conditions and whether BWU affects lower extremity muscle activation levels. Oxygen uptake, heart rate (HR) and surface electromyography (EMG) of vastus medialis (VM) and biceps femoris (BF) of 10 frail older women (mean +/- SD; 78 +/- 3.6 years) and 10 healthy older women (78.5 +/- 4.2 years) were measured during various walking conditions overground and on a treadmill with BWU. Frail older women exercising at their self-selected comfortable walking speed on the treadmill at 0% BWU had a higher walking energy cost per unit of time (WECt) compared to overground walking at the same speed (255 +/- 46 vs 207 +/- 32 J kg(-1) min(-1) P < 0.05), whereas healthy older women had similar responses in the two conditions (262 +/- 31 vs 260 +/- 39J kg(-1) min(-1)). However, WECt of treadmill walking at self-selected fast walking speed with 40% BWU was not statistically different to overground walking at comfortable walking speed for frail (218 +/- 36 vs 207 +/- 31 J kg(-1) min(-1)) or healthy older women (265 +/- 65 vs 262 +/- 32 J kg(-1) min(-1)). EMG of the VM and BF muscles did not significantly change in either group during treadmill walking at any speeds up to 40% BWU (P > 0.05). Frail older women could therefore be safely trained on a treadmill with 40% BWU thus achieving faster speeds without increasing energy and cardiac cost and without compromising lower extremity muscle activation levels. (C) 2010 Elsevier B.V. All rights reserved.