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Zemková, E, Cepková, A, Uvaček, M, and Šooš, L. A novel method for assessing muscle power during the standing cable wood chop exercise. J Strength Cond Res 31(8): 2246-2254, 2017-The study estimates the repeatability and sensitivity of a novel method for assessing (a) the maximal power during the standing cable wood chop exercise with different weights and (b) the endurance of the core muscles. A group of 23 fit men performed (a) maximal effort single repetitions of the standing cable wood chop exercise with weights increasing stepwise up to 1 repetition maximum (1RM) and (b) a set of 20 repetitions at a previously established weight at which maximal power was achieved. Results showed that mean power during the standing cable wood chop exercise is a reliable parameter, with intraclass correlation coefficient values above 0.90 for all weights tested. It was also shown to be a sensitive parameter able to discriminate within-group differences in the maximal power and endurance of core muscles. Substantial individual differences were found in mean power, especially at higher weights, and in the maximal power achieved at about 75% of 1RM (462.2 ± 57.4 W, n = 11), 67% of 1RM (327.2 ± 49.7 W, n = 7), and 83% of 1RM (524.0 ± 63.2 W, n = 5). At these weights, there were also significant differences between the initial and the final repetitions of the wood chop exercise (13.9%, p = 0.025; 10.2%, p = 0.036; and 13.8%, p = 0.028, respectively). These findings indicate that evaluation of the maximal power and endurance of the core muscles during the standing cable wood chop exercise on a weight stack machine is a reliable method and sensitive to differences among physically active individuals.

Background Although low back fatigue is an important intervening factor for physical functioning among sedentary people, little is known about its possible significance in relation to the spinal posture and compensatory postural responses to unpredictable stimuli. This study investigates the effect of lumbar muscle fatigue on spinal curvature and reactive balance control in response to externally induced perturbations. Methods A group of 38 young sedentary individuals underwent a perturbation-based balance test by applying a 2 kg load release. Sagittal spinal curvature and pelvic tilt was measured in both a normal and Matthiass standing posture both with and without a hand-held 2 kg load, and before and after the Sørensen fatigue test. Results Both the peak anterior and peak posterior center of pressure (CoP) displacements and the corresponding time to peak anterior and peak posterior CoP displacements significantly increased after the Sørensen fatigue test (all at p < 0.001). A lumbar muscle fatigue led to a decrease of the lumbar lordosis in the Matthiass posture while holding a 2 kg load in front of the body when compared to pre-fatigue conditions both without a load (p = 0.011, d = 0.35) and with a 2 kg load (p = 0.000, d = 0.51). Also the sacral inclination in the Matthiass posture with a 2 kg additional load significantly decreased under fatigue when compared to all postures in pre-fatigue conditions (p = 0.01, d = 0.48). Contrary to pre-fatigue conditions, variables of the perturbation-based balance test were closely associated with those of lumbar curvature while standing in the Matthiass posture with a 2 kg additional load after the Sørensen fatigue test (r values in range from −0.520 to −0.631, all at p < 0.05). Conclusion These findings indicate that lumbar muscle fatigue causes changes in the lumbar spinal curvature and this is functionally relevant in explaining the impaired ability to maintain balance after externally induced perturbations. This emphasizes the importance for assessing both spinal posture and reactive balance control under fatigue in order to reveal their interrelations in young sedentary adults and predict any significant deterioration in later years.

This study evaluates the effect of 8 weeks of the stable and unstable resistance training on muscle power. Thirty-three healthy men recreationally trained in resistance exercises, randomly assigned into two groups, performed resistance exercises either under stable or unstable conditions for 8 weeks (three sessions per week). Before and after 4 and 8 weeks of the training, they underwent squats and chest presses on either a stable surface or on a BOSU ball and a Swiss ball respectively with increasing weights up to at least 85% 1RM. Results showed significant improvements of mean power during chest presses on a Swiss ball at weights up to 60.7% 1RM after 4 and 8 weeks of the instability resistance training. Mean power increased significantly also during squats on a BOSU ball at weights up to 48.1% 1RM after 4 but not 8 weeks of instability resistance training. However, there were no significant changes in mean power during bench presses and squats on a stable support surface after the same training. These findings indicate that there is no cross effect of instability resistance training on power produced under stable conditions. This confirms and complies with the principle for specificity of training.

This study compares the differences in peak and mean power in the acceleration, as well as over the entire concentric phase of jumps and squats performed with and without countermovement (i.e. delta power) in athletes of different specializations. The participants performed either barbell squats or barbell jumps with and without countermovement bearing a weight of 70% 1RM. Results identified a significantly higher delta mean power in the entire concentric phase of jumps than in squats for high jumpers (29.8%, p=0.009) and volleyball players (24.3%, p=0.027). More specifically, their values were significantly higher during jumps in indoor volleyball players but not in beach volleyball players. On the other hand, rock & roll performers exhibited a significantly higher delta mean power during squats than jumps (19.5%, p=0.034) but this was only evident in those who specialized in acrobatics as opposed to dance. However, the values did not differ significantly during either jumps or squats for hockey players (9.5%, p=0.424) and karate competitors (11.6%, p=0.331). A similar trend was observed for peak and mean power in the acceleration phase of jumps and squats. It may be concluded then, that enhancement of power in the concentric phase of jumps and squats bearing an external load, differs in athletes with diverse demands on the explosive strength of their lower limbs. For most athletes, jumping may be considered a more specific alternative for the estimation of the