Ground Reaction Forces Are Predicted with Functional and Clinical Tests in Healthy Collegiate Students

Increased vertical and posterior ground reaction forces (GRFs) are associated with anterior cruciate ligament (ACL) injury. If a practical means to predict these forces existed, ACL injury risk could be attenuated. Forty-two active college-age individuals (21 females, 20.66 ± 1.46 y, 70.70 ± 2.36 cm, 82.20 ± 7.60 kg; 21 males, 21.57 ± 1.28 y, 65.52 ± 1.87 cm, 64.19 ± 9.05 kg) participated in this controlled laboratory study. GRFs were ascertained by having the subjects perform a unilateral landing task onto a force plate. Several clinical measures (Fat Free Mass (FFM), dorsiflexion passive range of motion (DPROM), isometric peak force of the lateral hip rotators, knee flexor/extensor peak force ratio (H:Q), the completion of the overhead deep squat), two functional tests (Margaria–Kalamen, Single Leg Triple Hop (SLTH)), and sex served as the predictor variables. Regression models to predict the GRFs normalized to the FFM (nGRFz, nGRFy) were generated. nGRFz was best predicted with a linear regression equation that included SLTH and DPROM (adjusted R² = 0.274; p = 0.001). nGRFy was best predicted with a linear regression equation that included H:Q, FFM, and DPROM (adjusted R² = 0.476; p < 0.001). Simple clinical measures and functional tests explain a small to moderate amount of the variance associated with the FFM normalized vertical and posterior GRFs in active college-age individuals.

A Bilateral Comparison of the Underlying Mechanics Contributing to the Seated Single-Arm Shot-Put Functional Performance Test

CONTEXT

Functional performance tests (FPTs) are tools used to assess dynamic muscle strength and power. In contrast to the lower extremity, fewer FPTs are available for the upper extremity. The seated single-arm shot put test has the potential to fill the void in upper extremity FPTs; however, the underlying mechanics have not been examined and, therefore, the validity of bilateral comparisons is unknown.

OBJECTIVE

To examine the effects of upper extremity dominance and medicine-ball mass on the underlying mechanics of the seated single-arm shot put.

DESIGN

Crossover study.

SETTING

Biomechanics laboratory.

PATIENTS OR OTHER PARTICIPANTS

Fifteen women (age = 23.6 ± 2.1 years, height = 1.65 ± .07 m, mass = 68.1 ± 11.7 kg) and 15 men (age = 24.3 ± 4.0 years, height = 1.80 ± 0.06 m, mass = 88.1 ± 16.4 kg), all healthy and physically active.

INTERVENTION(S)

Seated single-arm shot-put trials using the dominant and nondominant limbs were completed using three 0.114-m-diameter medicine-ball loads (1 kg, 2 kg, 3 kg).

MAIN OUTCOME MEASURE(S)

Customized touch-sensitive gloves, synchronized with kinematic data of the hands, signaled ball release, so that release height, release angle, and peak anterior and vertical velocity could be quantified for each trial. In addition, the horizontal range from release to first floor impact was recorded.

RESULTS

The dominant-limb horizontal ranges were 7% to 11% greater ( P < .001) than for the nondominant limb for each of the 3 ball masses. No bilateral release-height or -angle differences were revealed ( P ≥ .063). Release velocities were 7.6% greater for the dominant limb than the nondominant limb ( P = .001).

CONCLUSIONS

Our results support the use of the seated single-arm shot put test as a way to compare bilateral upper extremity functional performance. The near-identical release heights and angles between the dominant and nondominant limbs support the interpretation of measured bilateral horizontal-range differences as reflecting underlying strength and power differences.

Bilateral comparison of propulsion mechanics during single-leg vertical jumping

The primary purpose of this investigation was to compare single leg vertical jump performance and several performance characteristics derived from vertical ground reaction forces (vGRF) between the dominant (DOM) and nondominant (NDOM) legs. Secondary purposes included determining the relationship between the kinetic and temporal characteristics and single leg vertical jump performance and establishing the intrasession and intersession reliability of the characteristics considered. After a standardized warm-up, 20 physically active young adults (10 men, 10 women) performed three single leg DOM and three single leg NDOM vertical jumps in a random order during two sessions separated by three days. vGRF collected during each trial were used to calculate jump height, peak vertical power, peak vGRF, vGRF impulse, ratio between negative to positive vGRF impulse, time between maximum peak power to takeoff and countermovement depth. There were no significant differences between DOM and NDOM for jump height (p = .145) as well as the six characteristics considered (p > .05). There was a strong, direct relationship between jump height and peak vertical power for both DOM (r = .915, p < .001) and NDOM (r = .944, p < .001). With the exception of vGRF negative/positive impulse ratio, all dependent variables demonstrated moderate to high intrasession and intersession reliability. These results support using a single leg vertical jump protocol for conducting bilateral lower extremity functional assessments. With the exception of impulse ratio, the reliability results support using the protocol for serial assessments. In conclusion, healthy individuals can be expected to exhibit near equal single leg vertical jumping performance bilaterally, providing practitioners with a basis to interpret performance.