Muscle-Specific Effective Mechanical Advantage and Joint Impulse in Weightlifting

Lifting greater loads during weightlifting exercises may theoretically be achieved through increasing the magnitudes of net joint impulses or manipulating the joints’ effective mechanical advantage (EMA). The purpose of this study was to investigate muscle-specific EMA and joint impulse as well as impulse-momentum characteristics of the lifter-barbell system across a range of external loads during the execution of the clean. Collegiate-level weightlifters performed submaximal cleans at 65, 75, and 85% of their 1-repetition maximum (1-RM) while data from a motion analysis system and a force plate were used to calculate lifter-barbell system impulse and velocity, as well as net extensor impulse generated at the hip, knee, and ankle joints and the EMA of the gluteus maximus, hamstrings, quadriceps, and triceps surae muscles. The results indicated that the lifter-barbell system impulse did not change as load increased, whereas the velocity of the lifter-barbell system decreased with greater load. In addition, the net extensor impulse at all joints increased as load increased. The EMA of all muscles did not, however, change as load increased. The load-dependent effects on the impulse-velocity characteristics of the lifter-barbell system may reflect musculoskeletal force-velocity behaviors, and may further indicate that the weightlifting performance is limited by the magnitude of ground reaction force impulse. In turn, the load-dependent effects observed at the joint-level indicated that lifting greater loads were due to greater net extensor impulses generated at the joints of the lower extremity and not greater EMAs of the respective extensor muscles. In combination, these results suggest that lifting greater external loads during the clean is due to the ability to generate large extensor joint impulses, rather than manipulate EMA

NEURAL NETWORK PREDICTION OF BARBELL KINEMATICS FROM JOINT KINETICS IN WEIGHTLIFTING

The purpose of this study was to develop and train neural networks (NN) to predict barbell motion and velocity from hip, knee, and ankle joint torques during a weightlifting exercise. Seven weightlifters performed two repetitions of the clean exercise at 85% of maximum while reaction forces and 3-D motion data of the lifter and barbell were acquired. An inverse dynamics procedure was then used to calculate torques at the hip, knee, and ankle joints. The joint torque time-series data were used as inputs to two seperate NN to predict 1) the horizontal and vertical barbell trajectories and 2) the vertical barbell velocities. Both NN demonstrated low mean square errors and good agreement with experimental data, which suggests NN could be used to inform weightlifters and their coaches about the relationships between joint kinetics and barbell kinematics

IDENTIFYING JOINT-SPECIFIC LIMITATIONS AND TARGETS FOR IMPROVING WEIGHTLIFTING PERFORMANCE

The purpose of this study was to determine the relative effort (RE) of the extensor and plantarflexor muscles during the pull phase of the clean. Five weightlifters performed the clean at 85% of their one-repetition maximum while motion capture and ground reaction forces were recorded and used to calculate lower body net joint moments via inverse dynamics (NJMID). Joint angle and angular velocity data were used as input to a musculoskeletal model that estimated maximum NJM (NJMmax) weightlifters could theoretically generate. The RE of the hip and knee extensor and ankle plantarflexor muscles were calculated as the ratios between NJMID and NJMmax. The results suggest that the knee extensor muscles operate close to max capacity during both pull phases, and that the plantarflexor muscles operate close to their max capacity during the second pull

STRETCH-SHORTENING CYCLE FUNCTION OF THE KNEE EXTENSOR MUSCLE-TENDON UNIT DURING THE POWER CLEAN

The purpose of this case study was to investigate the stretch-shortening cycle behaviour of the knee extensor muscle-tendon unit during the power clean exercise. Kinematic and kinetic were acquired as a skilled weightlifter performed several repetitions of the power clean at 85% of 1-Repetition Maximum. Knee joint angular velocity, moment, and power time-series during the pull-phase of the power clean were calculated and used to delineate between concentric and eccentric movement phases. The analysis of the kinematic time-series data showed knee extension-flexion-extension movement pattern, whereas the analysis of the kinetic data showed that the movement pattern consisted of dynamic concentric and eccentric sequences, which highlighted stretch-shortening cycle behavior of the knee extensors, and surprisingly also the knee flexor, muscle groups

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

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

Spectral Properties of H-Reflex Recordings After an Acute Bout of Whole-Body Vibration

Although research supports the use of whole-body vibration (WBV) to improve neuromuscular performance, the mechanisms for these improvements remain unclear. The purpose of this study was to identify the effect ofWBV on the spectral properties of electrically evoked H-reflex recordings in the soleus (SOL) muscle. The H-reflex recordings were measured in the SOL muscle of 20 participants before and after a bout of WBV. The H-reflexes were evoked every 15 seconds for 150 seconds after WBV. A wavelet procedure was used to extract spectral data, which were then quantified with a principle components analysis. Resultant principle component scores were used for statistical analysis. The analysis extracted 1 principle component associated with the intensity of the myoelectric spectra and 1 principle component associated with the frequency. The scores of the principle component that were related to the myoelectric intensity were smaller at 30 and 60 milliseconds after WBV than before WBV. The WBV transiently decreased the intensity of myoelectric spectra during electrically evoked contractions, but it did not influence the frequency of the spectra. The decrease in intensity likely indicates a smaller electrically evoked muscle twitch response, whereas the lack of change in frequency would indicate a similar recruitment pattern of motor units before and after WBV

INDUCED ACCELERATION ANALYSIS IN WEIGHTLIFTING: A PILOT STUDY

The purpose of this pilot study was to determine the functional roles of the lower extremity joints during a weightlifting exercise. One participant performed the power clean exercise with 75% of one-repetition maximum while 3D motion capture and force plate data were recorded. Net joint moments were calculated via inverse dynamics analysis and used as inputs to an induced acceleration analysis that calculated joint-specific contributions to ground reaction forces (GRF). Results showed that all joints exhibited to phase-specific contributions to vertical GRF. Interestingly, the ankle plantarflexors produced primarily anterior GRF, whereas the knee extensors produced primarily posterior GRF. The results underscore joint- and phase-specific contributions to the production of vertical and horizontal GRF during the power clean

Patterns of Barbell Acceleration during the Snatch in Weightlifting Competition

The purpose of this study was to determine the association between weightlifting performance and vertical barbell acceleration patterns. Barbell kinematic time-series data were tracked from 18 snatches from six weightlifters during a regional weightlifting competition. These data were used to calculate vertical barbell accelerations. Time-series data were normalised to 100% of lift phase, defined as the time interval between barbell lift-off and maximum height of the barbell during each snatch lift. The time-series data were then entered into a pattern recognition algorithm that extracted principal patterns and calculated principal pattern scores. Body mass-normalised lift weight, which was used to quantify weightlifting performance, was significantly correlated (r = 0.673; P = 0.033) with a pattern that captured a difference in peak vertical barbell acceleration between the transition and the second pull phase. This correlation indicated that barbell acceleration profiles of higher weight snatch lifts were characterised by smaller decreases in acceleration during the second knee bend and smaller peak acceleration during the second pull phase. Weightlifting coaches and sports scientist should monitor and track vertical acceleration of the barbell, with focus on acceleration profiles that limit (1) deceleration during the transition phase between the first and second pull and (2) peak acceleration during the second pull phase of the snatch

Prediction of Throwing Distance in the Men’s and Women’s Javelin Final at the 2017 IAAF World Championships

The purpose of this study was to use regularised regression models to identify the most important biomechanical predictors of throwing distance in elite male (M) and female (F) javelin throwers at the 2017 IAAF world championships. Biomechanical data from 13 male and 12 female javelin throwers who competed at the 2017 IAAF world championships were obtained from an official scientific IAAF report. Regularised regression models were used to investigate the associations between throwing distance and release parameters, whole-body kinematic and joint-level kinematic data. The regularised regression models identified two biomechanical predictors of throwing distances in both M and F javelin throwers: release velocity and knee flexion angle of the support leg at the moment of javelin release. In addition, the length of the delivery stride was an important predictor of throwing distance in M throwers, whereas the javelin’s attitude angle and the distance between the whole-body centre of mass and the centre of mass of the back foot at the beginning of the delivery phase were important predictors of throwing distance in F throwers