Is there a connection between individual thigh muscle volume and squat lifting velocity
Authors: Knopfli Céline Raquel , Achermann Basil , Lorenzetti Silvio , Oberhofer Katja 
Published: February 2023

Background
Identifying key musculoskeletal and biomechanical criteria that are associated with Resistance Training (RT) is essential to avoid injury and optimise training outcome. Biomechanically, so-called velocity-based RT is an objective approach to directly quantify training intensity and effect. From a musculoskeletal perspective, RT enhances muscle force, which is correlated to the muscle’s physiological cross-sectional area, and thus muscle volume.
Goal
The goal of this study is to find out whether there exists a correlation between the change in lifting velocity during a squat set-to-exhaustion and the Hamstring to Quadriceps Muscle Volume Ratio (H/Q Ratio) as indicator of muscle strength.
Methodology
Ethical approval for this study was given by the Kantonale Ethikkommission Bern. Recreationally trained RT athletes (age 20-40years) were recruited through the investigator’s network. The methodology is divided into three parts. Firstly, the hamstring and quadriceps muscle volumes are determined using Magnetic Resonance Imaging (MRI) as gold standard. Thereby, the open-source software SASHIMI with an automatic tracking function is utilised to segment the MRI data. The segmented data is further processed with the Python programming language to derive the H/Q ratios. Secondly, lifting velocity during the squat is determined using data from optical motion capture (Vicon Nexus System with 10 infrared cameras) as gold standard. Thereby, a set-to-exhaustion is performed at 80% of each individual one repetition maximum (1RM), whereby the subjects are asked to complete the concentric phase at maximum speed to comply with velocity-based RT recommendations. Lifting velocity is derived from the tracked position of two reflective markers on the bar using the Python programming language. Thirdly, a statistical correlation analysis is conducted between the musculoskeletal and the biomechanical parameters. Statistical analysis is performed with the statistical analysis software R, with the level of significance set at p = 0.05.
Results
To date, MRI data have been acquired in five athletes and the corresponding muscle volumes have been determined (Quadriceps: 0.00525 +/-0.00185 m3 and Hamstrings: 0.0019 +/-0.007 m3). In addition, the load-velocity profiles have been derived in the same group of subjects. The MRI-based muscle volumes are in a similar range to previously published data (Maeo et al., 2021). Furthermore, the results of the load-velocity profiles show the anticipated decrease according to velocity-based RT guidelines (Rodriguez-Rosell et al., 2020).
Discussion
In a next step further data will be acquired in more subjects for subsequent statistical analysis. The outcome of the present study is expected to provide new scientific insights into the relationship between musculoskeletal and biomechanical criteria that affect squat performance. The insight may help to optimize velocity-based RT recommendations for individual athletes to maximise performance and reduce injury risks.
References
Rodríguez-Rosell, D., Yáñez-García, J. M., Sánchez-Medina, L., Mora-Custodio, R., & González-Badillo, J. J. (2020). Relationship between velocity loss and repetitions in Reserve in the bench press and back squat exercises. Journal of Strength and Conditioning Research, 34(9), 2537–2547. https://doi.org/10.1519/JSC.0000000000002881
Maeo, S., Huang, M., Wu, Y., Sakurai, H., Kusagawa, Y., Sugiyama, T., Kanehisa, H., & Isaka, T. (2021). Greater hamstrings muscle hypertrophy but similar damage protection after training at long versus short muscle lengths. Medicine & Science in Sports & Exercise, 53(4), 825–837. https://doi.org/10.1249/MSS.0000000000002523