Power during functional tests in older adults: reliability, reference values and relationship to other sarcopenia-related outcomes

Aging is associated with declines in lower-limb muscle strength and power. Muscle power (i.e., force x velocity) starts to decline earlier in life and at a faster rate compared to muscle mass and strength. Low values of muscle power in old age have been associated with mobility limitations and mortality, stressing the importance to include muscle power assessments to prevent these negative outcomes. Lower-limb power is typically measured with specialized and expensive exercise equipment that requires skilled lab personnel (e.g., pneumatic or isotonic resistance machines, force plate analysis, Nottingham Power Rig) and is often limited to single joint movements (e.g., isokinetic dynamometers). These measurements are unable to capture the complex functioning of muscles in daily life activities and large-scale applicability in clinical settings is limited. Clinically feasible measurements of lower-limb power should be easy to administer, limited in time, low cost, functionally relevant and suitable for elderly. In this regard, simple field tests, such as sit-to-stand and stair-climbing tests, are preferable. In addition to accurate timing, inertial measurement units can provide information on sub-phase durations and kinematic properties of a functional movement. Previously, researchers have used sensor-based trunk kinematics to estimate the vertical power required to elevate the body’s center of mass during a transfer from sit to stand with a single sensor worn at the waist. Recently, we have used a similar approach to evaluate power during stair ascent in healthy adults (20-70 years). Results showed that stair ascent power is strongly related to leg-extensor power (r = 0.80), underlining the added value of sensor-based analysis of power over duration parameters (r = -0.53 with leg-extensor power).
However, the reliability of the method, its sensitivity to detect age-related differences and its link to other sarcopenia-related outcomes remains to be investigated. In addition, many clinical settings have limited space or no access to a full flight of stairs. A simple standardized stair model of 3 steps with fixed dimensions would improve applicability in clinical settings. To our knowledge, no research has investigated the potential of a sensor-based analysis of stair ascent power on a 3-step stair model.