The influence of arm swing constraint on thigh kinematics, heart rate response, and perceived exertion during the two-minute step test

Holding a smartphone against the thigh provides a simple means of instrumenting the Two-Minute Step Test (2MST), but it constrains arm swing and may affect movement, cardiovascular responses, and perceived exertion. This study examined whether holding a smartphone against the thigh during the 2MST alters thigh kinematics, heart rate response, or perceived exertion in healthy young adults. Forty-five participants (27 men and 18 women; 19.5 ± 2.6 years) performed the 2MST under two counterbalanced conditions: unrestricted arm swing, with the smartphone secured to the right thigh using an elastic pouch, and constrained arm swing, with the smartphone held against the right thigh and the opposite hand placed on the contralateral thigh. Smartphone gyroscope data were used to determine step cycles, mean thigh peak angular velocity, cycle duration, variability, and the rate of change in thigh peak angular velocity. Heart rate response and perceived exertion were also recorded. Paired comparisons were performed using appropriate tests with Bonferroni correction. Step cycle counts were similar between constrained and unrestricted conditions (131 ± 20 vs 127 ± 19 cycles; p = 0.091). Mean thigh peak angular velocity, cycle duration, rate of change in thigh peak angular velocity, cycle duration variability, and heart rate response did not differ between conditions. Thigh peak angular velocity variability was higher in the constrained condition (p < 0.01; effect size = 0.68). Perceived exertion was also slightly higher in the constrained condition (12.6 ± 1.8 vs 11.9 ± 2.1; p = 0.024), but the difference was below the minimal detectable change threshold. These findings indicate that holding a smartphone against the thigh does not meaningfully alter overall 2MST performance, most thigh kinematic outcomes, or heart rate response, supporting this practical smartphone-based protocol.