Christopher F. Geiser

The effect of remote voluntary contractions on knee extensor torque.

PURPOSE Concurrent activation potentiation (CAP) is purported to enhance the force capabilities of muscles via the contraction of muscles remote to the prime mover. This phenomenon has been described as remote voluntary contractions (RVC). The objective of this study was to assess a variety of RVC and their effect on isometric knee extensor torque to evaluate the existence of CAP. METHODS Twelve males who regularly participated in lower body resistance training served as subjects. Subjects performed maximum voluntary isometric contractions (MVIC) of the knee extensors without RVC, as well as in a variety of conditions that included RVC, in a randomized order. The RVC conditions included jaw clenching, bilateral gripping, jaw clenching combined with contralateral gripping and the Valsalva maneuver, and the combination of jaw clenching, bilateral gripping, and the Valsalva maneuver. RESULTS A repeated-measures ANOVA revealed significant main effects (P = 0.001) for RVC condition. Bonferroni-adjusted post hoc analysis identified several differences in RVC compared with the NO-RVC condition (P < 0.05). The RVC condition including jaw clenching, bilateral gripping, and the Valsalva maneuver resulted in approximately 14.6% and 14.8% greater average and peak torque, respectively, compared with the NO-RVC condition. CONCLUSIONS These findings indicate that RVC augment torque, which may be useful during the performance of resistance training as well as athletic tasks that require acute maximal strength. These findings support the existence of the CAP phenomenon.

Ulnar stress fracture of the nondominant arm in a tennis player using a two-handed backhand.

Stress fractures are infrequently seen in non-weight-bearing bones. However, stress fractures may be present in any bone that undergoes repetitive stress. We report an unusual case of stress fracture in the nondominant arm of a tennis player who uses a two-handed backhand stroke.

Hip External Rotator Strength Is Associated With Better Dynamic Control of the Lower Extremity During Landing Tasks

Abstract Malloy, PJ, Morgan, AM, Meinerz, CM, Geiser, CF, and Kipp, K. Hip external rotator strength is associated with better dynamic control of the lower extremity during landing tasks. J Strength Cond Res 30(1): 282–291, 2016—The purpose of this study was to determine the association between hip strength and lower extremity kinematics and kinetics during unanticipated single-leg landing and cutting tasks in collegiate female soccer players. Twenty-three National Collegiate Athletic Association division I female soccer players were recruited for strength testing and biomechanical analysis. Maximal isometric hip abduction and external rotation strength were measured using a hand-held dynamometer and expressed as muscle torque (force × femoral length) and normalized to body weight. Three-dimensional lower extremity kinematics and kinetics were assessed with motion analysis and force plates, and an inverse dynamics approach was used to calculate net internal joint moments that were normalized to body weight. Greater hip external rotator strength was significantly associated with greater peak hip external rotation moments (r = 0.47; p = 0.021), greater peak knee internal rotation moments (r = 0.41; p = 0.048), greater hip frontal plane excursion (r = 0.49; p = 0.017), and less knee transverse plane excursion (r = −0.56; p = 0.004) during unanticipated single-leg landing and cutting tasks. In addition, a statistical trend was detected between hip external rotator strength and peak hip frontal plane moments (r = 0.39; p = 0.06). The results suggest that females with greater hip external rotator strength demonstrate better dynamic control of the lower extremity during unanticipated single-leg landing and cutting tasks and provide further support for the link between hip strength and lower extremity landing mechanics.

Anticipatory Effects on Lower Extremity Neuromechanics During a Cutting Task

CONTEXT Continued research into the mechanism of noncontact anterior cruciate ligament injury helps to improve clinical interventions and injury-prevention strategies. A better understanding of the effects of anticipation on landing neuromechanics may benefit training interventions. OBJECTIVE To determine the effects of anticipation on lower extremity neuromechanics during a single-legged land-and-cut task. DESIGN Controlled laboratory study. SETTING University biomechanics laboratory. PARTICIPANTS Eighteen female National Collegiate Athletic Association Division I collegiate soccer players (age = 19.7 ± 0.8 years, height = 167.3 ± 6.0 cm, mass = 66.1 ± 2.1 kg). INTERVENTION(S) Participants performed a single-legged land-and-cut task under anticipated and unanticipated conditions. MAIN OUTCOME MEASURE(S) Three-dimensional initial contact angles, peak joint angles, and peak internal joint moments and peak vertical ground reaction forces and sagittal-plane energy absorption of the 3 lower extremity joints; muscle activation of selected hip- and knee-joint muscles. RESULTS Unanticipated cuts resulted in less knee flexion at initial contact and greater ankle toe-in displacement. Unanticipated cuts were also characterized by greater internal hip-abductor and external-rotator moments and smaller internal knee-extensor and external-rotator moments. Muscle-activation profiles during unanticipated cuts were associated with greater activation of the gluteus maximus during the precontact and landing phases. CONCLUSIONS Performing a cutting task under unanticipated conditions changed lower extremity neuromechanics compared with anticipated conditions. Most of the observed changes in lower extremity neuromechanics indicated the adoption of a hip-focused strategy during the unanticipated condition.

Mechanical Demands of the Hang Power Clean and Jump Shrug: A Joint-level Perspective

Abstract Kipp, K, Malloy, PJ, Smith, J, Giordanelli, MD, Kiely, MT, Geiser, CF, and Suchomel, TJ. Mechanical demands of the hang power clean and jump shrug: a joint-level perspective. J Strength Cond Res 32(2): 466–474, 2018—The purpose of this study was to investigate the joint- and load-dependent changes in the mechanical demands of the lower extremity joints during the hang power clean (HPC) and the jump shrug (JS). Fifteen male lacrosse players were recruited from a National Collegiate Athletic Association DI team, and completed 3 sets of the HPC and JS at 30, 50, and 70% of their HPC 1 repetition maximum (1RM HPC) in a counterbalanced and randomized order. Motion analysis and force plate technology were used to calculate the positive work, propulsive phase duration, and peak concentric power at the hip, knee, and ankle joints. Separate 3-way analysis of variances were used to determine the interaction and main effects of joint, load, and lift type on the 3 dependent variables. The results indicated that the mechanics during the HPC and JS exhibit joint-, load-, and lift-dependent behavior. When averaged across joints, the positive work during both lifts increased progressively with external load, but was greater during the JS at 30 and 50% of 1RM HPC than during the HPC. The JS was also characterized by greater hip and knee work when averaged across loads. The joint-averaged propulsive phase duration was lower at 30% than at 50 and 70% of 1RM HPC for both lifts. Furthermore, the load-averaged propulsive phase duration was greater for the hip than the knee and ankle joint. The joint-averaged peak concentric power was the greatest at 70% of 1RM for the HPC and at 30%–50% of 1RM for the JS. In addition, the joint-averaged peak concentric power of the JS was greater than that of the HPC. Furthermore, the load-averaged peak knee and ankle concentric joint powers were greater during the execution of the JS than the HPC. However, the load-averaged power of all joints differed only during the HPC, but was similar between the hip and knee joints for the JS. Collectively, these results indicate that compared with the HPC the JS is characterized by greater hip and knee positive joint work, and greater knee and ankle peak concentric joint power, especially if performed at 30 and 50% of 1RM HPC. This study provides important novel information about the mechanical demands of 2 commonly used exercises and should be considered in the design of resistance training programs that aim to improve the explosiveness of the lower extremity joints.

Reactive Strength Index Modified Is a Valid Measure of Explosiveness in Collegiate Female Volleyball Players.

Abstract Kipp, K, Kiely, MT, and Geiser, CF. Reactive strength index modified is a valid measure of explosiveness in collegiate female volleyball players. J Strength Cond Res 30(5): 1341–1347, 2016—The purpose of this study was to investigate the validity of the reactive strength index modified (RSImod) as a measure of lower body explosiveness. Fifteen female, National Collegiate Athletic Association Division I volleyball players performed vertical countermovement jumps (CMJs) while standing on a force plate. Each player performed 3 CMJs. The vertical ground reaction forces collected during each jump were used to calculate jump height, time to take-off, time to peak force, peak force, peak rate of force development, and peak power; the latter 3 variables were all normalized to body mass. Reactive strength index modified was calculated as the ratio between jump height and time to take-off. All variables, except for jump height, were then entered a factor analysis, which reduced the input data into 2 factors: a force factor and a speed factor. Although RSImod loaded more strongly onto the force factor, further analysis showed that RSImod loaded positively onto both force and speed factors. Visual analysis of the Cartesian coordinates also showed that RSImod loaded into the quadrant of greater force and speed abilities. These results indicate that the construct of RSImod, as derived from CMJ force-time data, captures a combination of speed-force factors that can be interpreted as lower body explosiveness during the CMJ. Reactive strength index modified therefore seems to be a valid measure to study lower body explosiveness.

Predicting net joint moments during a weightlifting exercise with a neural network model

The purpose of this study was to develop and train a Neural Network (NN) that uses barbell mass and motions to predict hip, knee, and ankle Net Joint Moments (NJM) during a weightlifting exercise. Seven weightlifters performed two cleans at 85% of their competition maximum while ground reaction forces and 3-D motion data were recorded. An inverse dynamics procedure was used to calculate hip, knee, and ankle NJM. Vertical and horizontal barbell motion data were extracted and, along with barbell mass, used as inputs to a NN. The NN was then trained to model the association between the mass and kinematics of the barbell and the calculated NJM for six weightlifters, the data from the remaining weightlifter was then used to test the performance of the NN - this was repeated 7 times with a k-fold cross-validation procedure to assess the NN accuracy. Joint-specific predictions of NJM produced coefficients of determination (r2) that ranged from 0.79 to 0.95, and the percent difference between NN-predicted and inverse dynamics calculated peak NJM ranged between 5% and 16%. The NN was thus able to predict the spatiotemporal patterns and discrete peaks of the three NJM with reasonable accuracy, which suggests that it is feasible to predict lower extremity NJM from the mass and kinematics of the barbell. Future work is needed to determine whether combining a NN model with low cost technology (e.g., digital video and free digitising software) can also be used to predict NJM of weightlifters during field-testing situations, such as practice and competition, with comparable accuracy.