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Background: Heat is a major form of stress caused by exercise, though its value in driving adaptation is not well understood. Aim: Through a contralateral-limb control study we examined whether supplemental heating of active muscle during resistance training differentially affected physical and functional adaptations compared to those from traditional training without muscle heating. Methods: Ten healthy young adult volunteers (5 females) completed 12-wk progressive resistance training of the knee extensors, comprising 30 sessions of 32 repetitions (4 sets of 8) of unilateral knee extensions at 70% of legspecific 1-RM. One randomly allocated thigh was heated during and for 20 min after each training session, using a customised heat pad eliciting muscle temperatures of 38-39.5 °C. Thigh lean mass was measured at baseline and 12 weeks, and concentric knee extensor maximal isokinetic (90°.s-1) torque was measured at baseline and each 4 wk. Results: Quadriceps' lean mass increased across 12-wk training, by 15 ±7% (761 ±280 g; p=0.00) and 15 ±6% (752 ±304 g; p=0.00) in the heated and control limbs, respectively; the difference being trivial (0 ±3%; p=0.94). Peak torque increased (p=0.02) to more extent, by 33 ±38% and 35 ±37%, respectively; with an unclear difference of 2 ±17% between limbs (p=0.82). Rate of torque development increased by 47 ±44% in the heated limb (p=0.01) and 45 ±39% (p=0.08) in the control limb (difference: 2 ±18%; p=0.90). No sex differences were evident for mass or strength changes. Conclusions: Heating of the active muscle mass during and after resistance training shows no clear positive (or negative) effect on training-induced hypertrophy or the improvements in concentric isokinetic strength and rate of torque development, compared to those from resistance training without heat. [ABSTRACT FROM AUTHOR]