Tailoring exercise intensity: Acute and chronic effects of constant-speed and heart rate-clamped exercise in healthy, inactive adults

OBJECTIVES: This study tested whether speed-controlled exercise prescriptions result in greater external training load and acute cardiorespiratory responses at the end of exercise compared to heart rate-controlled prescriptions, despite equivalent intensity at the start of exercise. It also investigated whether speed-controlled prescriptions lead to greater improvements in cardiorespiratory fitness after 8 weeks of training. DESIGN: A two-group, randomized block design with repeated testing sessions. METHODS: Thirty-four healthy, inactive adults were randomized into two groups. One group trained at a constant speed set midway between the first and second lactate thresholds, whereas the other trained at the corresponding heart rate. Both groups performed 30 min of continuous exercise three times per week for 8 weeks. Speed, heart rate, and oxygen consumption were measured at the end of the first session and later time points for complementary analysis. Peak treadmill speed and maximal oxygen consumption were assessed before and after the intervention. RESULTS: At the end of the first session, the speed group showed higher values compared to the heart rate group for speed (1.5 km/h), heart rate (22 bpm), and oxygen consumption (6.0 mL/kg/min) (all p < 0.001). Similarly, adaptive changes were greater in the speed group, with a larger increase in peak treadmill speed (0.9 km/h, p < 0.001) and maximal oxygen consumption (1.2 mL/kg/min, p = 0.01). CONCLUSIONS: These findings indicate that the exercise intensity reference method influences acute responses and chronic adaptations to exercise in healthy, inactive adults.