Author(s): BEHAN, F., BALSHAW, T., JAMES, L., FUNNELL, M., MCDERMOTT, E., FOLLAND, J. , Institution: TRINITY COLLEGE DUBLIN, Country: IRELAND, Abstract-ID: 2405

INTRODUCTION:
The relationship between muscle size and strength is well established,1 but the relationship of these variables with tendon size has not been clearly elucidated. Strength training results in disproportionate increases in muscle strength (larger) compared to muscle hypertrophy (moderate), and much smaller/marginal increases in tendon cross-sectional area,2 suggesting that these variables do not scale. Thus, the relationship of tendon size with both muscle size and muscle strength requires investigation. Consequently, we aimed to investigate the relationships between patellar tendon (PT) cross-sectional area (CSA) and quadriceps femoris (QF) maximum anatomical CSA (QF ACSAmax), and PT CSA and knee extensor maximum voluntary torque.
METHODS:
Fifty-seven healthy, young, and recreationally active young men (age: 26 ± 5 years, body mass: 75 ± 11 kg, height: 179 ± 8 cm) were recruited for this study. Isometric maximum voluntary contractions of the knee extensors were assessed with a custom-built isometric knee extension dynamometer to determine isometric muscle strength (maximum voluntary torque) at a knee joint angle of 104°. Magnetic resonance imaging (3.0 T Discovery MR750w, GE Healthcare, Chicago, IL) of the dominant thigh and knee and subsequent manual segmentation allowed determination of quadriceps femoris anatomical cross-sectional area (axial slice thickness 5 mm; inter-slice gap 15 mm) and patellar tendon cross-sectional area (axial slice thickness 2 mm; inter-slice gap 0 mm). Relationships between PT size with both muscle size and strength were assessed by Pearson’s correlation coefficient with an α level of 0.05.
RESULTS:
There was a strong correlation between QF ACSAmax and isometric knee extension strength (r = 0.779, p < 0.001), as expected. However, PT CSA was only weakly correlated with QF ACSAmax (r = 0.312, p = 0.018) and isometric knee extension strength (r = 0.322, p = 0.014). The muscle/tendon area ratio (i.e. QF ACSAmax divided by patellar tendon CSA) ranged from 54.2 to 139.4 (i.e. a 2.6-fold difference between smallest and largest ratio) and had a between participant coefficient of variation of 18.0%.
CONCLUSION:
Despite the strong association between muscle strength and size, the association between tendon size and strength, and tendon size and muscle size appears much weaker. Whether individuals with disproportionately large muscles relative to their tendon are more likely to develop tendon pathology requires further prospective evaluation.

References
1. Balshaw TG, at al. Med Sci Sports Exerc. 2021 Oct 1;53(10):2140-2151.
2. Massey GJ, et al. Acta Physiol (Oxf). 2018 Apr;222(4):e13019.
3. Szaro P, Ghali Gataa K. Sci Rep. 2021 Mar 17;11(1):6131.