A blood lactate-based graded exercise test protocol for evaluating physiological response to wearable robots

When wearable robots (WRs) are designed for daily use, their physiological burden on the wearer should be assessed using reliable parameters under standardised conditions. This study introduces a Graded Exercise Test (GXT) protocol employing blood lactate concentration (BLC) as the primary evaluation metric. Seventeen-participants performed a treadmill-based GXT twice with progressive speed and incline, once without load and once while carrying a simulated 10% body-weight load. During each test, heart rate (HR) and oxygen uptake (VO₂) were continuously monitored, and BLC was measured every two minutes throughout the protocol. Results showed that BLC displayed nonlinear dynamics revealing exercise intensity transitions through lactate thresholds. While VO₂ changed proportionally with workload, BLC increased earlier under loading conditions, reflecting metabolic perturbations associated with anaerobic activation. These findings demonstrate that the proposed BLC-based evaluation protocol provides more sensitive indicators of fatigue and metabolic strain than conventional measures when assessing the physiological demands imposed by WRs.