(23) Relationship between Vertical Ground Reaction Force during Isometric Squat at Various Knee Angles and Dynamic 1RM Back Squat in College-Aged Females

Despite recent attempts of various isometric assessments to predict athletic performances, limited information on such assessments in females is available.  A back-squat exercise is one of the most important exercise to enhance athletic performances for the lower body arguably.  

Purpose: The purpose of this investigation was to systematically examine the relationship between a dynamic one repetition maximum (1 RM) squat weight obtained and peak vertical ground reaction forces (vGRFs) at five different knee angles (thighs are parallel to the floor (IsoPara), 90°(Iso90), 100°(Iso100), 110°(Iso110), and 120°(Iso120)) during the maximum isometric squat exercise in recreationally trained college-aged females.

Methods: Ten recreationally weight-trained healthy college-aged female subjects (mean age = 22.40 ± 2.01 years) were recruited from the University of Nebraska-Lincoln campus community for this study. Each subject’s back squat 1RM assessments were conducted twice and mean value was used for analysis. A force plate was used to analyze the vGRFs during the experimental sessions. For a maximum isometric squat, an order of the 5 angles was randomly assigned, and the subjects performed at least two trials for each angle to ensure the reliability (two trials’ peak vGRF must be within 250 N). The subjects were instructed to push an immovable bar fixed on a squat rack as fast and forcefully as possible for 5 seconds. The subjects were given a 3-5 minute break between experimental trials.

Results: Person product-moment correction coefficients revealed that the correlations between the 1RM weight mean values and mean maximum isometric squat peak vGRFs at all of the knee angles were significantly correlated (p ≤ 0.05).  In order to identify a multicollinearity issue among the independent variables, variance inflation factors (VIFs) were calculated.  To address the high VIFs found for all of the isometric vGRFs at the various knee angles, only the highest correlation coefficient found (r = 0.95) during the knee angle at 90° was used for a linear regression analysis. The analysis generated a regression equation to predict 1RM dynamic back squat weight based on the peak ground reaction force during maximum isometric squat at the knee angle of 90° (Y = -114.97 + 0.73X) which explains 89% of variance to predict the 1RM squat weight (Adjusted R Squared = 0.89). 

Conclusions: The 1RM weights lifted for the back-squat exercise in college-aged females and the peak vGRFs obtained from the force plate during maximum isometric squat at the knee angle of 90° were strongly correlated.  The peak vGRF at the knee angle of 90° during the isometric back squat may be used to predict healthy college-aged females’ dynamic 1 RM weights. PRACTICAL APPLICATIONS: When a force plate or other similar device is available for strength and conditioning coaches and other exercise professionals the isometric peak vGRF may be used not only for tracking individuals’ progressions but also predicting an appropriate amount of weight used for their dynamic squat exercise.

Acknowledgements: None