Purpose: To determine how the rest interval (RI) lengths of 30 and 90 s between sets of biceps curl exercise affect the total volume of work performed and serum CK activity, and to verify the relationship between inter-individual variability of CK activity and total volume performed when the resistance exercise bout is conducted with 30 or 90 s Methods: Twenty-seven healthy sedentary men (18À20 years old) volunteered to participate in this study and were divided into two groups: 30RI (n ¼ 16) or 90RI (n ¼ 11), based on the RI length of 30 or 90 s between the sets of a resistance exercise protocol. The one repetition maximum (1RM) assessment of the elbow flexion was carried out and then a resistance exercise protocol which constituted five sets of biceps curl at 85% of 1RM with 30-s Correspondence to: . Downloaded from www.worldscientific.com by MONASH UNIVERSITY on 08/25/15. For personal use only.(30RI group) or 90-s (90RI group) RI length between sets was performed. Each bout was performed to voluntary fatigue and the number of repetitions and workout volume completed were calculated. Subjects provided blood samples prior to resistance exercise, and at 48 and 96 h following exercise to evaluate serum CK activity. The inter-individual serum CK activity along the 96 h after exercise was analyzed. Results: The results demonstrated that the longer RIs provided greater workout volume as expected, but there were no differences in serum CK activity between the groups. Additionally, it was possible to identify two high responder subjects, one from each RI group, who showed a great interindividual serum CK activity variability. Conclusion: Exercising with short RIs does not appear to present any additional muscle microtrauma to untrained subjects. Further studies are necessary to evaluate if the inter-individual variability of the serum CK activity is influenced by the inter-set RI length.

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Objectives: Plyometrics has been used in sports training and many aspects of this modality are poorly understood. This study measures the magnitude of variations of serum creatine kinase (CK) activity and perceived muscle soreness after one session of Countermovement Jump (CMJ) session and compares 1 and 3 minutes rest intervals between each sets.Methods: A group of 30 young male was dividing in two groups and performed ten sets of ten CMJ with 1 or 3 minutes rest interval between sets. Before and after session (24, 48, and 72-h) they informed the muscle soreness perception and blood samples were collected for dosage of serum CK activity. Two (time) x Two (treatment) ANOVA was used to test differences in serum CK activity and muscle soreness. The alpha level was set at 0.05.Results: Serum CK activity measured 48 h after session augments ~2 and ~1.5 times in 1 min and 3 min rest interval respectively. No significant difference between groups that rests 1 or 3 minutes between sets was found. Muscle soreness rises 24 h after session without significant differences between groups.Conclusions: The findings show that the CMJ increases perceived muscle soreness and increases the serum CK activity, and the intervals of rest do not modulate these variables.