Effects of four days of isokinetic training on isometric and isokinetic peak torque and muscle cross-sectional area in women

Background Short-term resistance training provides insights into the early phase adaptations of muscular strength and muscle cross-sectional area (CSA). The purpose of this study was to examine the effects of 2, 3, and 4 days of maximal, concentric, reciprocal isokinetic forearm extension (FE) and forearm flexion (FF) training at 180°∙s−1 on peak torque (PT) during maximal voluntary isometric contractions (MVIC) and isokinetic muscle actions at 60, 180, and 300°∙s−1, and changes in muscle CSA in untrained women.Methods Twelve women (Mean ± SD: age: 21.7 ± 1.2 yrs; height: 167.9 ± 5.2 cm; body mass: 64.7 ± 6.8 kg) completed 4 days of maximal, concentric, reciprocal isokinetic FE and FF training at 180°∙s−1 for 6 sets of 10 repetitions with the non-dominant arm (based on throwing preference). In addition, the subjects completed 4 testing visits (Pre-testing and following 2 [Day2], 3 [Day3], and 4 [Day4] days of training) with the non-dominant arm that included 2 FE and 2 FF MVICs (elbow at 90°), followed by 3, maximal, concentric, reciprocal isokinetic FE and FF muscle actions at 60°∙s−1, 180°∙s−1, and 300°∙s−1. Changes in PT were assessed using separate 4 (Velocity: MVIC, 60°∙s−1, 180°∙s−1, and 300°∙s−1) ×4 (Time: Pretest, Day2, Day3, and Day4) repeated measures ANOVAs for FE and FF. Changes in CSA were assessed using separate 2 (Muscle: Triceps Brachii and Biceps Brachii) ×4 (Time: Pretest, Day2, Day3, and Day4) repeated measures ANOVAs. An alpha value of p ≤ 0.05 was used for all ANOVAs. Follow-up pairwise comparisons were used when necessary.Results For FE PT (decomposed by Velocity), Day2 (28.0 ± 8.3 Nm;p = 0.036, d = 0.563) and Day4 (28.4 ± 9.3 Nm;p = 0.042, d = 0.572) MVIC were greater than Pre-test (23.9 ± 6.1 Nm), and at 60°∙s−1, Day4 FE PT was greater (24.3 ± 9.2 Nm;p = 0.015, d = 0.304) than Day2 (21.8 ± 7.1 Nm). For FF PT (collapsed across Velocity), Day3 (29.6 ± 6.2 Nm;p = 0.006, d = 0.0.190) and Day4 (31.1 ± 6.8 Nm;p < 0.001, d = 0.409) were greater than Day2 (28.4 ± 6.4 Nm), and Day3 (p = 0.018, d = 0.377) and Day4 (p < 0.001, d = 0.593) were greater than Pretest (27.3 ± 6.0 Nm). In addition, Day4 FF PT (31.1 ± 6.8 Nm) was greater (p = 0.007, d = 0.231) than Day3 (29.6 ± 6.2 Nm). For CSA (collapsed across Muscle), Day2 (4.56 ± 0.75 cm2;p = 0.006, d = 0.408), Day3 (4.59 ± 0.73 cm2;p = 0.004, d = 0.455), andDay4 (4.61 ± 1.0 cm2;p = 0.025, d = 0.400) were greater than Pretest (4.27 ± 0.69 cm2).Conclusions A minimum of 3 days of isokinetic training is needed for untrained women to see improvements in isometric and isokinetic strength and increases in the CSA of the non-dominant arm.