413 International Journal of Sport Nutrition and Exercise Metabolism, 2005, 15, 413-424 © 2005 Human Kinetics, Inc. The authors are with the School of Life Sciences, Kingston University, Kingston-upon-Thames, KT1 2EE, United Kingdom. Supplementation with β-Hydroxy- β-Methylbutyrate (HMB) and α-Ketoisocaproic Acid (KIC) Reduces Signs and Symptoms of Exercise- Induced Muscle Damage in Man Ken A. van Someren, Adam J. Edwards, and Glyn Howatson This study examined the effects of β-hydroxy- β-methylbutyrate (HMB) and α-ketoisocaproic acid (KIC) supplementation on signs and symptoms of exercise-induced muscle damage following a single bout of eccentrically biased resistance exercise. Six non-resistance trained male subjects performed an exercise protocol designed to induce muscle damage on two separate occa- sions, performed on the dominant or non-dominant arm in a counter-balanced crossover design. Subjects were assigned to an HMB/KIC (3 g HMB and 0.3 g α-ketoisocaproic acid, daily) or placebo treatment for 14 d prior to exercise in the counter-balanced crossover design. One repetition maximum (1RM), plasma creatine kinase activity (CK), delayed onset muscle soreness (DOMS), limb girth, and range of motion (ROM) were determined pre-exercise, at 1h, 24 h, 48 h, and 72 h post-exercise. DOMS and the percentage changes in 1RM, limb girth, and ROM all changed over the 72 h period (P < 0.05). HMB/KIC supplementation attenuated the CK response, the percentage decrement in 1RM, and the percentage increase in limb girth (P < 0.05). In addition, DOMS was reduced at 24 h post-exercise (P < 0.05) in the HMB/KIC treatment. In conclu- sion, 14 d of HMB and KIC supplementation reduced signs and symptoms of exercise-induced muscle damage in non-resistance trained males following a single bout of eccentrically biased resistance exercise. Key Words: eccentric exercise, creatine kinase, DOMS β-hydroxy-β-methylbutyrate (HMB) is a metabolite of the branch chain amino acid leucine and its ketoacid α-ketoisocaproate (32). HMB has been used as a dietary supplement to increase carcass quality in livestock (31) and has recently gained popularity as a dietary supplement in humans, particularly among strength athletes (27, 28). Today, many commercial HMB supplements also contain a small amount of α-ketoisocaproic acid (KIC). In man, the reported benefits of supplementation with dosages of between 1.5 and 3.0 g/d HMB include reduced muscle protein degradation and consequent 06VanSomeren(413) 413 8/10/05, 8:40:40 AM