Poster P13 - Knee Kinematics in Male and Female Hexagonal Barbell Squat Jumps: A Statistical Parametric Mapping (SPM) Approach

Introduction: Power and force output are important metrics for success from athletic competition to functional strength. Often the goal of training is to develop these characteristics and focus on modalities that elicit positive adaptations relative to these parameters. The hexagonal barbell is a variation of the traditional barbell that is used in lower-extremity exercises, and has beneficial effects on peak force, peak power output, and rate of force development. Strength and conditioning practices require individualization to achieve the best results, and the differences between males and females are an important dynamic to consider. Sex-specific responses to training modalities are a highly studied comparison, but often the model for statistical analysis is discrete. It is challenging to determine an appropriate, a priori analysis methodology given the complexity of time-series data; and spaciotemporal hypotheses are limited by these same constraints. For this reason, continuous statistical models are useful. Statistical Parametric Mapping (SPM) is one of the tools available that allows researchers to address these issues. Statistical Parametric Mapping uses Random Field Theory to perform topological inference instead of performing separate tests at each time point, which introduces an inflation of Type I error. The advantage of this is the entire 1D field can be evaluated for an indirect hypothesis test without ad-hoc assumptions.
The purpose of this study was to evaluate the differences between males and females knee torques longitudinally using SPM during the concentric phase in the flexion/extension (X), varus/valgus (Y), and internal/external rotation (Z) planes for loaded hexagonal barbell squat jumps.

Materials and

Methods: 10 male subjects and 7 females subjects volunteered and signed consent for this study. Study was approved by the IRB review board at Illinois State University. A 10-camera Vicon markered motion-capture system sampling at 200hz was used to capture kinematic data. Two AMT force plates sampling at 1000hz captured ground reaction forces. Subjects performed 3 bodyweight (BW) hexagonal barbell squat jumps, followed by a random order of 20% 1RM and 40% 1RM hexagonal barbell squat jumps. The left knee torque (Nm/Kg) in the X (flexion/extension), Y (abduction/adduction), and Z (internal/external rotation) planes were evaluated for all trials. For this study, kinematic and kinetic data was limited to the concentric phase of the jump. Onset of concentric phase was measured as the minimum vertical value of the sacrum marker or calculated COM, and end of concentric phase was when the vertical ground reaction force was measured to be < 4N. Force plate and marker coordinate data was filtered in Vicon using a 4th order Butterworth with cutoff frequencies of 300hz and 6hz, respectively. Data was then exported to Visual3D where an 8-segment, lower limb model estimate joint forces and torques using standard inverse dynamic techniques. The data were then time-normalized representing 0-100% and averaged across the 3 trials for each subject. The time-normalized data series were used as input for the SPM analysis. Statistical parametric mapping was implemented in MATLAB. Significance was set a priori at p< 0.05.

Results, Conclusions, and Discussions: Joint torques had non-significant differences between males and females for the X and Y plane (flexion/extension, abduction/adduction) in the bodyweight condition. Joint torques in the Z direction (internal/external rotation) demonstrated a significant, momentary difference between genders (p = 0.049). This difference, however, was not measurable temporally across the concentric phase, and the magnitude of the significance level relative to the a priori alpha level of 0.05 would indicate this represented a single time-series measurement. Joint torques in the 20% 1RM condition showed significant differences in the X plane from the 0-60% time-normalized concentric phase (p < 0.001), and significant differences in the Z plane from 0-80% of concentric phase (p < 0.001). Graphs of Z plane knee torque showed an inverse relationship in magnitude of toque throughout movement. Joint torques in the 40% 1RM condition showed significant differences in the X plane from the 0-70% concentric phase (p < 0.001), and significant differences in the Z plane from 0-80% of concentric phase (p < 0.001). Similar to the 20% condition, the 40% condition elicited an inverse, bodyweight-normalized toque magnitude throughout the concentric phase. SPM can be an important tool to visualize topological inferences over a time series of data instead of performing separate inferential tests at discrete points in time. The kinematic responses between males and females remained nearly Identical across all trials in the Y (abduction/adduction) plane but were significantly different in both the X (flexion/extension) and Z (internal/external rotation) planes in each of the loaded conditions. There was a demonstrably different kinematic adaptation to loading conditions between males and females, and the differences were observed to be throughout a majority of the concentric phase, with temporal ranges measured from 0 to 60-70% in the X plane, and 0 to 80% in the Z plane. Recognizing the magnitude and sequencing of differences in kinematic strategies between males and females is useful for the development of safe and effective strength and conditioning protocols.

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