In-flight resistive exercise workouts are performed on novel flywheel-based hardware. Designs of such workouts may be better served by measuring changes to lactate and testosterone values. To make workouts pertinent to μg they should utilize unique features of flywheel-based hardware, such as the option to exert eccentric torque. Our study compares changes to blood lactate and testosterone concentrations ([BLa-], [T]) from leg press workouts that differ by contractile mode and work volume, on a flywheel ergometer. Subjects performed three workouts; two entailed two sets of concentric-eccentric (CE2) or concentric-only (CO2) actions. A third involved four sets of concentric-only actions (CO4). Workouts entailed eight-repetition sets with 90-second rest periods. Total work (TW) was quantified per workout. [T] were assessed, both pre- and post-exercise. [BLa-] were measured pre- and at 0-, 5-, 10-, 15-, and 20-minutes post-exercise. TW was assessed with a one-way analysis of variance (ANOVA). [BLa-] and [T] were evaluated with two- and three-factor ANOVAs, respectively. Scheffe’s test was our post-hoc. TW data had an inter-workout (CE2, CO4 > CO2) difference. [BLa-] included a two-way interaction as CO4 workouts evoked higher post-exercise values. Results for [T] produced gender (men > women) and time (post > pre) main effects. Our results imply flywheel-based workouts with a large volume of concentric actions evoke no greater increase in [T] than workouts with only half the muscle shortening activity, despite attainment of higher TW and post-workout [BLa-].