Correlations Between Internal and External Power Outputs During Weightlifting Exercise

Identifying loads that maximize mechanical power is important because training at such loads may optimize gains in dynamic athletic performance. The purpose of this study was to examine correlations between measures of external mechanical power output and internal mechanical joint power output across different loads during a weightlifting exercise. Ten subjects performed 3 sets of the clean exercise at 65, 75, and 85% of 1 repetition maximum (1RM). Peak external mechanical power output was calculated with 4 commonly used methods, whereas an inverse dynamics approach was used to calculate peak internal mechanical power output for the hip, knee, and ankle joints along with the peak of the sum of all internal joint powers. All peak mechanical power outputs were expressed as relative peak power by either ratio (watts per kilogram) or allometrically scaling to body mass (W·kg-0.67). Correlation coefficients were used to compare power output measures. The greatest numbers of significant correlations between internal and external power outputs were observed at 85% of 1RM, at this load hip and knee joint power outputs were correlated to external mechanical power output when calculated with the traditional work-energy method. In addition, the peak sum of all mechanical joint powers was correlated to mechanical power output when calculated with the impulse-momentum method at loads of 75 and 85% of the 1RM. Allometric scaling of power outputs yielded one more significant correlation than did the ratio scaled power outputs. These findings support the use of the work-energy method when making inferences about internal joint powers from external power outputs when loads equal to 85% of 1RM are being lifted. In addition, the impulse-momentum method may be used to make inferences about the sum of all internal joint powers from external power outputs when loads between 75 and 85% of 1RM are being lifted

Lower Extremity Biomechanics During Weightlifting Exercise Vary Across Joint and Load

The purpose of this study was to determine the effect of load on lower extremity biomechanics during the pull-phase of the clean. Kinematic and kinetic data of the three joints of the lower extremity were collected while participants performed multiple sets of cleans at three percentages: 65, 75, and 85% of 1-Reptition maximum (RM). General linear models with repeated measures were used to assess the influence of load on angular velocities, net torques, powers, and rates of torque development at the ankle, knee, and hip joint. The results suggest that the biomechanical demands required from the lower extremities change with the lifted load and to an extent depend on the respective joint. Most notably, the hip and knee extended significantly faster than the ankle independent of load, while the hip and ankle generally produced significantly higher torques than the knee. Torque, rate of torque development, and power at the ankle and knee joint were maximal at 85% and 75% of 1-RM, respectively, whereas torque and rate of torque development at the hip were maximal at loads above 75% and 85% of 1-RM, respectively. This study provides important novel information about the mechanical demands of a weightlifting exercise and should be heeded in the design of resistance training programs

Energy Flow Analysis to Investigate Youth Pitching Velocity and Efficiency

Purpose The purposes of this study were 1) to investigate the transfer of energy through the kinetic chain by youth baseball pitchers during the pitching motion and 2) to provide insight into how the total magnitude of energy flow and its linear and rotational components relate to both velocity and joint torque per unit increment of pitch velocity (joint load efficiency). Methods Twenty-four youth baseball pitchers participated in this study. Data collection occurred in an indoor research laboratory equipped with a 14-camera infrared motion capture system and an instrumented pitcher’s mound with embedded force plates. Energy flow was calculated by integrating power transfer into and out of each segment. The magnitudes of key instances of energy flow were compared to pitch velocity and velocity-normalized joint torques using simple linear regressions. Results All of the energy flow variables calculated had a significant correlation to pitch velocity. Energy flow into the arm from the trunk had the strongest correlation to velocity of any variable investigated (r = 0.900, P = 0.000). The total magnitude of energy flow into the trunk had a significant correlation to increased horizontal shoulder adduction efficiency and shoulder internal rotation efficiency. The magnitude of energy flow into the trunk by only joint forces had a significant correlation to increased horizontal shoulder adduction efficiency, shoulder internal rotation efficiency, and elbow varus efficiency. Conclusions Energy flow analysis is an effective tool providing quantitative assessment of the kinetic chain to gain a deeper understanding of how energy moves through an athlete, and how specific pitching mechanics impact this movement. The results of this study support the importance of generating energy flow throughout the body to produce high velocities and energy flow through the trunk to increase pitch efficiency

Effect of Loading Condition on Traction Coefficient Between Shoes and Artificial Turf Surfaces

Background. The interaction between a shoe and a turf surface is highly complex and difficult to characterize. Over the three decades since artificial turf was introduced, researchers have attempted to understand the traction caused by the interaction. However, some of the methodologies used for traction measurements have not capitalized on advances in currently available technology for testing and most testing conditions have not simulated realistic physiological loads. Method of Approach. To assess the effect of test condition on traction results, the newly designed TurfBuster testing device was used to collect traction data on FieldTurf™ brand artificial turf under varying conditions. Four cleated athletic shoes were tested under eight different vertical loads ranging from 222-1780 N. The static, dynamic, and peak traction coefficient values were calculated and averaged over three trials for each shoe and condition. Results. In all but the lowest vertical load condition, the static traction coefficient was less than the dynamic traction coefficient. There was a distinct separation found between 666 N and 888 N loading conditions for all three variables measured. Below the load condition of 666 N only one significant difference was found in all comparisons across and within shoe styles. Above 888 N multiple differences were found across shoe styles, but differences were not found within a shoe style until a load of at least 1554 N. Conclusions. At loads below 666 N the cleats perform almost identically at all three variables measured, static, dynamic, and peak traction coefficients. At loads above 888 N, shoe traction was different among the cleat styles for all traction variables. However, at loads between 888 N and 1334 N there were no differences found within a shoe style. This implies that each shoe has no performance difference in loads representative of up to one bodyweight. Due to these results the measurement of traction characteristics between cleated shoes and FieldTurf should be conducted at a load of at least 888 N to determine differences across shoe styles and loads ranging from 888 N to at least 1554 N to determine individual shoe characteristics

A New Method to Quantify Demand on the Upper Extremity During Manual Wheelchair Propulsion

Objective To use an ergonomics-based rating that characterizes both demand on, and capacity of, upper-extremity muscle groups during wheelchair propulsion to help identify the muscle groups most at risk for pain or overuse injury in a relatively demanding wheelchair propulsion task. Design Case series. Setting Biomechanics research laboratory. Participants Sixteen manual wheelchair users with complete (American Spinal Injury Association grade A) T6-L2 paraplegia. Interventions Not applicable. Main outcome measures Internal peak joint moments required by each of the major upper-extremity muscle groups for propelling a wheelchair up a ramp; isometric strength of each of the muscle groups in positions simulating wheelchair propulsion; and wheelchair propulsion strength rating (WPSR) for each muscle group, calculated by normalizing the joint demands to their capacity. Results The largest joint moment was for shoulder flexion, at 39.7±13.9Nm. Shoulder flexion also accounted for the peak WPSR value of 66.5%±20.3%. Supination and pronation movements had low peak moment requirements (3.4Nm, 5.0Nm, respectively) but high WPSR values (41%, 53%, respectively). Conclusions Even a relatively benign ramp (2.9°) places a large demand on the musculature of the upper extremity, as assessed by using the WPSR to indicate muscular demand

Valgus Torque in Youth Baseball Pitchers: A Biomechanical Study

The purpose of this study was to determine the biomechanical and anthropometric factors contributing to elbow valgus torque during pitching. Video data of 14 youth pitchers throwing fastballs were used to calculate shoulder and elbow kinematics and kinetics. Peak elbow valgus torque averaged 18 Nm and occurred just before maximal shoulder external rotation. The magnitude of valgus torque was most closely correlated with the thrower\u27s weight. When subject weight and height were controlled for, maximum shoulder abduction torque and maximum shoulder internal rotation torque were most strongly associated with elbow valgus torque, accounting for 85% of its variance (P \u3c .001). When only kinematic variables were considered, maximum shoulder external rotation accounted for 33% of the variance in valgus torque. Given that the biomechanical variables correlated with peak valgus torque are not easily modifiable, limiting the number of innings pitched is likely the best way to reduce elbow injury in youth pitchers