1 The purpose of this study was to compare the kinematic, metabolic, endocrine, and perceptual 2 responses of three back squat protocols with equal loads, number of repetitions, and total rest 3 duration. Eight strength-trained men performed 36 back squats using 75% 1RM and 420 s of 4 total rest during basic cluster sets of 4 (CS4), rest-redistribution sets of 4 (RR4), and rest-5 redistribution sets of 1 (RR1). Ratings of perceived exertion (RPE), blood lactate (La), mean 6 velocity maintenance

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... (MVM), and mean velocity loss (MVL) were measured during exercise. 7 Total testosterone (TT), growth hormone (GH), cortisol (C), and sex-hormone binding globulin 8 (SHBG) were measured before exercise and 15, 30, and 60 min post-exercise. There were no 9 differences between protocols for MVM. However, MVL was less during RR1 compared to RR4 10 (p=0.032), and neither protocol was different than CS4. All protocols resulted in similar 11 increases in RPE and La, which remained elevated up to 30 min post-exercise (p<0.05). In all 12 protocols, GH increased and returned to baseline by 60 min post-exercise (p<0.05). At 60 min 13 post-exercise, TT was less than all other time points (p<0.05). There were no main effects for 14 time for SHBG or C. The data from this study show that different types of cluster set protocols 15 can result in pro-anabolic physiological responses to resistance training. Additionally, coaches 16 can redistribute rest periods without affecting perceived effort or metabolic and hormonal 17 changes if the external load, number of repetitions, and total rest time are equalized. 18 Physiological responses to cluster sets 2 42 velocity, greater power output, greater jump height) compared to TS (7, 20, 30, 34, 43). In 43 A C C E P T E D Copyright ª 2017 National Strength and Conditioning Association Physiological responses to cluster sets 3 addition to the positive effects of CS on acute performance, research has indicated that 44 implementing less-fatiguing protocols during training can result in similar strength gains 45 compared to more fatiguing protocols (6, 18, 19). Although these studies indicate that large 46 amounts of fatigue may not be necessary to induce gains in strength, it should not be forgotten 47 Oliveira PR. Comparison between constant and decreasing rest intervals: influence on maximal 399 strength and hypertrophy. J Strength Cond Res 24: 1843-1850, 2010. 400 4. Denton J and Cronin JB. Kinematic, kinetic, and blood lactate profiles of continuous and intraset 401 rest loading schemes. J Strength Cond Res 20: 528-534, 2006. 402 5. Fleck SJ and Kraemer WJ. Designing Resistance Training Programs, Fourth Edition. Champaign, 403 IL: Human Kinetics, 2014. 404 6. Folland JP, Irish CS, Roberts JC, Tarr JE, and Jones DA. Fatigue is not a necessary stimulus for 405 strength gains during resistance training. Physiological responses to cluster sets 20 7. Girman JC, Jones MT, Matthews TD, and Wood RJ. Acute effects of a cluster-set protocol on 407 hormonal, metabolic and performance measures in resistance trained males. Eur J Sport Sci 14: 408 151-159, 2014. 409 8. Godfrey RJ, Madgwick Z, and Whyte GP. The exercise-induced growth hormone response in 410 athletes. Sports Med 33: 599-613, 2003. 411 Appl Physiol 69: 1442-1450, 1990. 449 23. Kraemer WJ, Noble BJ, Clark MJ, and Culver BW. Physiologic responses to heavy-resistance 450 exercise with very short rest periods. Int J Sports Med 8: 247-252, 1987. 451 24. Kraemer WJ and Ratamess NA. Hormonal responses and adaptations to resistance exercise and 452 training. Physiological responses to cluster sets 22 25. Krieger JW. Single vs. mulitple sets of resistance exercise for muscle hypertrophy: a meta-454 analysis.