Validation Of Smartphone-based Assessment Of Sit-to-stand Power

Abstract

Modern smartphones are inexpensive, portable, user friendly, and contain sensitive gyroscopes. Apps can be used to sample, store, and wirelessly transmit data. Although easy to conduct, field tests of sit-to-stand (STS) power provide only a relatively crude (timed or counted) outcome measure of global performance. Expensive lab-based biomechanics equipment is required to obtain measures of leg power (LP) for individual repetitions during brief 5x STS tasks. PURPOSE: To determine the ability of the iPod to detect movement speed for each rep during a 5x STS test, and make comparisons with an electrogoniometer (eGONI) and force platform. METHODS: Young adults (22.9 ± 2.9yrs, 21 men, 21 women) performed a 5x STS task as rapidly as possible with strict form. Three trials were performed. A 5th generation iPod Touch was firmly attached (Velcro) to a strap around the lower thigh. An eGONI (Biometrics) was placed laterally across the knee joint. The feet were on a force platform (AMTI Accusway) in front of the chair. Concurrently, iPod gyroscope data (rad), knee joint angle (rad), and ground reaction force (GRF, N) were sampled at 100Hz. The peak slope (0.1s time constant) of the iPod pitch signal, eGONI signal, and GRF was calculated for the rising phase of each rep. The peak GRF was also measured. The instantaneous slope was normalized to body mass to provide an index of power for each rep. For each device, the mean power of 5 reps and the maximal single rep value was calculated for the three trials. Correlations were computed between the devices across all subjects. RESULTS: The mean (R2=0.85) and max (R2=0.86) iPod peak slope were highly correlated with the corresponding eGONI value. The mean (R2=0.47) and max (R2=0.44) iPod peak slope were moderately correlated with the corresponding GRF value. The mean and max values were highly correlated with each other for the iPod (R2=0.99), eGONI (R2=0.99), and GRF (R2=0.98). The greater rising power for men vs. women was detected similarly by the iPod (32.5%), eGONI (29.5%), and peak GRF (30.9%). CONCLUSION: As measured with the iPod, mean rising power from the 5x STS is very reflective of a single maximal rep. The iPod is sufficiently sensitive to detect differences in chair rising power between sexes and can replace an electronic goniometer for assessing chair rising power.