Measuring power during the sit-to-stand transfer.

Power has been demonstrated to be an early and potent marker of frailty. The measurements currently available are tied to locality. Usually, measurements include single joint movements or movements of only the legs and the resistance is not adjusted for body weight. In this study, a portable method to measure power in the sit-to-stand transfer was developed and tested. Mean power was calculated from the vertical ground reaction force of body weight, the difference between height in a sitting and in an upright position and the time taken to stand up. The results of this power measurement were compared with an isokinetic force measurement, the "Nottingham power rig", and measurement of physical performance in a five-repetition chair rise (five-chair rise). A convenience sample of 33 healthy elderly subjects [mean (SD) age: 67.8 (6.7) years; 17 men, 16 women] was included. Measurement of power during the sit-to-stand transfer showed good correlation to isokinetic force measurement (r=0.68) and to the "Nottingham power rig" (r=0.6). Correlation to five-chair rise was poor (r=-0.08). In conclusion, the study shows that the method presented is able to measure power during performance of a daily task. The poor correlation between the introduced measurement and the five-chair rise suggests that it might be able to detect decline in muscle function earlier by the introduced measurement than by measurement of the functional status. As it is inexpensive and portable, its use in clinical practice and research contexts, including home-bound individuals, is feasible.