Sex differences in trunk, pelvis, hip and knee kinematics and eccentric hip torque in adolescents
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Bridgeman, LA, McGuigan, MR, Gill, ND, and Dulson, DK. Test-retest reliability of a novel isokinetic squat device with strength-trained athletes. J Strength Cond Res 30(11): 3261-3265, 2016-The aim of this study was to investigate the test-retest reliability of a novel multijoint isokinetic squat device. The subjects in this study were 10 strength-trained athletes. Each subject completed 3 maximal testing sessions to assess peak concentric and eccentric force (N) over a 3-week period using the Exerbotics squat device. Mean differences between eccentric and concentric force across the trials were calculated. Intraclass correlation coefficients (ICCs) and coefficients of variation (CVs) for the variables of interest were calculated using an excel reliability spreadsheet. Between trials 1 and 2 an 11.0 and 2.3% increase in mean concentric and eccentric forces, respectively, was reported. Between trials 2 and 3 a 1.35% increase in the mean concentric force production and a 1.4% increase in eccentric force production was reported. The mean concentric peak force CV and ICC across the 3 trials was 10% (7.6-15.4) and 0.95 (0.87-0.98) respectively. However, the mean eccentric peak force CV and ICC across the trials was 7.2% (5.5-11.1) and 0.90 (0.76-0.97), respectively. Based on these findings it is suggested that the Exerbotics squat device shows good test-retest reliability. Therefore practitioners and investigators may consider its use to monitor changes in concentric and eccentric peak force.
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Douglas, J, Pearson, S, Ross, A, and McGuigan, M. Effects of accentuated eccentric loading on muscle properties, strength, power, and speed in resistance-trained rugby players. J Strength Cond Res 32(10): 2750-2761, 2018-The purpose of this study was to determine the effects of slow and fast tempo resistance training incorporating accentuated eccentric loading (AEL) compared with traditional resistance training (TRT) in trained rugby players. Fourteen subjects (19.4 ± 0.8 years, 1.82 ± 0.05 m, 97.0 ± 11.6 kg, and relative back squat 1 repetition maximum [1RM]: 1.71 ± 0.24 kg·BM) completed either AEL (n = 7) or TRT (n = 7) strength and power protocols. Two 4-week phases of training were completed. The first phase emphasized a slow eccentric tempo, and the second phase emphasized a fast eccentric tempo. Back squat 1RM, inertial load peak power, drop jump reactive strength index (RSI), 40-m speed, maximum sprinting velocity (Vmax), and vastus lateralis (VL) muscle architectural variables were determined at baseline and after each phase of training. Slow AEL elicited superior improvements in back squat 1RM (+0.12 kg·BM; effect size [ES]: 0.48; and 90% confidence interval [CI]: 0.14, 0.82), 40-m time (-0.07 seconds; ES: 0.28; and CI: 0.01-0.55), and Vmax (+0.20 m·s; ES: 0.52; and CI: 0.18-0.86) vs. slow TRT. Fast AEL elicited a small increase in RSI but impaired speed. There was a likely greater increase in peak power with fast TRT (+0.72 W·kg; ES: 0.40; and CI: 0.00-0.79) vs. fast AEL alongside a small increase in VL pennation angle. The short-term incorporation of slow AEL was superior to TRT in improving strength and maximum velocity sprinting speed in rugby players undertaking a concurrent preparatory program. The second 4-week phase of fast AEL may have exceeded recovery capabilities compared with fast TRT.
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Traditional (TRAD) resistance training involves equal loading during the concentric and eccentric phases. Whereas eccentric-enhanced (ECC+) resistance training involves concentric and overloaded eccentric muscle actions, and purportedly results in greater muscle strength and mass than TRAD. PURPOSE: To test the hypothesis that ECC+ would result in greater muscle performance outcomes than TRAD after a five-week progressive resistance training program. METHODS: Twenty-two previously untrained males (22.1 ± 0.8 yrs) were randomized into training volume matched TRAD (4 sets × 6 reps at 52.5% 1RM) or ECC+ (3 sets × 6 reps at 40% 1RM concentric and 100% 1RM eccentric) groups. Participants performed chest press and squat exercise (3 × week-1) for five weeks. Training loads were increased for subsequent sessions upon successful completion of assigned repetitions. Chest and leg muscle strength [one repetition maximum (1RM)] and endurance (repetitions to fatigue) were assessed before and after the intervention. RESULTS: Muscle performance measures were similar between groups at baseline. Following the intervention, chest press (+10.1 % TRAD; +9.0% ECC+) and squat (+25.4% TRAD; +18.6% ECC+) muscle strength and chest press (+8.9% TRAD; +9.1% ECC+) and squat (+21.7% TRAD; +19.4% ECC+) endurance increased similarly between groups, respectively. Although matched at the onset of training, the total training volume over five-weeks was greater in the TRAD than the ECC+ group (83037 ± 4082 kg vs. 72458 ± 3164 kg, p<0.05), respectively. CONCLUSIONS: ECC+ may be a more efficient mode of training than TRAD, as muscle performance responses were similar between groups despite a lower total training volume in the ECC+ group.
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This study evaluated the ground reaction force (GRF) and rate of force development (RFD) of the back squat at 3 different loads. Twelve subjects performed the back squat with 80%, 100%, and 120% of their 1 repetition maximum (RM) on a force platform. A two way repeated measures ANOVA revealed significant main effects for GRF for both the eccentric (p ≤ 0.001) and concentric (p ≤ 0.001) phases but no interaction between phase and GRF or RFD (p < 0.05). No significant main effects were found for RFD for the eccentric (p = 0.09) and concentric phases (p = 0.38). Post hoc analyses demonstrated that back squats at 120% produced the highest GRF in the eccentric and concentric conditions. Mean RFD was highest, and trending toward significance, during the eccentric phase at 100% of 1 RM condition.
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The purpose of this study was to determine the acute effects of a spectrum of eccentric loads on force, velocity, and power during the concentric portion of maximal-effort jump squats utilizing a repeated measures design. Thirteen resistance-trained men (age = 22.8 ± 2.9 years, weight = 87.1 ± 11.8 kg, 163.5 ± 28.6 kg squat 1 repetition maximum [1RM]; mean ± SD), who routinely incorporated back squats into their training, participated as subjects in this investigation. Jump squat performance was assessed using 4 experimental conditions. The first of these conditions consisted of an isoinertial load equal to 30% of back squat 1RM. The remaining conditions consisted of jump squats with a concentric load of 30% 1RM, subsequent to the application of experimental augmented eccentric loading (AEL) conditions of 20, 50, and 80% of back squat 1RM, respectively. All subjects performed 2 sets of 1RM of maximum- effort jump squats with all experimental conditions in a counter- balanced sequence. Forty-eight hours after completing the first testing session, subjects repeated the experimental testing protocol to establish stability reliability. Peak performance values for the reliable variables of force, velocity, and power, as well as force and power values obtained at 20-ms intervals during the initial 400 ms of the concentric jump squat range of motion, showed no statistical difference (p > 0.05) across the experimental AEL loads. These results suggest that load-spectrum AEL prior to a 30% 1RM jump squat fails to acutely enhance force, velocity, and power.
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Munger, CN, Archer, DC, Leyva, WD, Wong, MA, Coburn, JW, Costa, PB, and Brown, LE. Acute effects of eccentric overload on concentric front squat performance. J Strength Cond Res 31(5): 1192-1197, 2017-Eccentric overload is used to enhance performance. The purpose of this study was to investigate the acute effects of eccentric overload on concentric front squat performance. Twenty resistance-trained men (age = 23.80 ± 1.82 years, height = 176.95 ± 5.21 cm, mass = 83.49 ± 10.43 kg, 1 repetition maximum [1RM] front squat = 131.02 ± 21.32 kg) volunteered. A dynamic warm-up and warm-up sets of front squat were performed. Eccentric hooks were added to the barbell. They descended for 3 seconds, until eccentric hooks released, and performed the concentric phase as fast as possible. There were 3 randomly ordered conditions with the concentric phase always at 90% 1RM and the eccentric phase at 105, 110, and 120% of 1RM. Two repetitions were performed for each condition. A repeated measures analysis of variance was used to determine differences. For peak velocity, there were main effects for time and condition (p < 0.05), where post (1.01 ± 0.10 m·s) was greater than pre (0.96 ± 0.11 m·s) and 120% (1.03 ± 1.11 m·s) was greater than 105% (0.99 ± 0.13 m·s). For peak power, there was a main effect for condition where 120% (2,225.00 ± 432.37 W) was greater than 105% (2,021.84 ± 563.53 W). For peak ground reaction force, there were main effects for time and condition, where post was greater than pre and 120% was greater than 105%. For the rate of force development, there was no interaction or main effects. Eccentric overload enhanced concentric velocity and power; therefore, it can be used by strength coaches and athletes during the power phase of a training program. It can also be used to prescribe supramaximal loads and could be a tool to supplement the clean exercise because the front squat is a precursor.
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1. Abstract 1.1. Introduction: Rotational movements of the trunk and pelvis are visible during activities of daily living. To date, no researchers have assessed the reliability of any test used to examine rotational mobility of the lower trunk-pelvis complex. The aim of the study was to assess the reliability of the Trunk-Pelvis-Hip Angle test. 1.2. Materials and Methods: The study included healthy 41 adolescents aged 12-15 . Measurements were performed by three experienced physiotherapists. 1.3. Results: Reliability was excellent for three observers. Intraclass correlation coefficient ranged from 0.894 to 0.938 for intraobserver reliability. The interobserver intraclass correlation coefficient ranged from 0.888 to 0.900 . 1.4. Conclusion: The Trunk-Pelvis-Hip Angle test is a reliable measurement and may be used for examining the range of the lower trunk-pelvis rotation in adolescents. The test provides a new possibility in diagnosing the musculoskeletal system. 2. Keywords: Adolescents; Pelvis; Range of Rotation; Reliability; Spine; Trunk 3. Abbreviations TPHA test : Trunk-Pelvis-Hip Angle test TPHA left : Trunk-Pelvis-Hip Angle test on the left side of the body TPHA right : Trunk-Pelvis-Hip Angle test on the right side of the body
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