Author(s): ANDO, R., OHNUMA, H., TANJI, F., IKEDA, T., YAMANAKA, R., SUZUKI, Y., Institution: JAPAN INSTITUTE OF SPORTS SCIENCES, Country: JAPAN, Abstract-ID: 1460

INTRODUCTION:
We recently reported a positive correlation between distance running time and cross-sectional area (CSA) of the quadriceps femoris (QF), suggesting that larger QF is associated with lower distance running performance (Ando et al. 2022). It is well known that distance running performance is strongly influenced by running economy. Running economy is related to vertical stiffness (Kvert) and/or leg stiffness (Kleg) (Li et al. 2019; Zhang et al. 2022) that reflect the storage and the reutilization of the elastic energy. Taken these findings together, we hypothesized that distance runners with lower competitive level cannot use the elastic energy (i.e., stretch-shortening cycles of the muscle-tendon unit) well during running; therefore, they are forced to produce active force from the QF, which eventually became hypertrophied. The purpose of this study was to examine the relationship between Kvert/Kleg during running and QF CSA in national-level distance runners.
METHODS:
Fifteen national-level male distance runners participated in the study (age: 25 ± 3 years; height: 171.6 ± 5.7 cm, body mass: 57.6 ± 3.5 kg, official personal best time for the 5000-m event: 13’45”11 ± 00’19”91). The participants were scanned in a supine position with a 3.0 T magnetic resonance image scanner and T1-weighted spin-echo transaxial images of the mid-thigh of the right leg were collected. The QF, hamstring (HM), and adductor (AD) muscles were identified and calculated their CSAs. The ratio of the muscle CSA to body mass to the two-thirds power was calculated as the relative muscle CSA (cm2/kg2/3). After individual warm-ups, the participants ran 60 m straight at an average velocity of their personal best time for 5000-m race on an all-weather track. The ground reaction force data were recorded using six force platforms. Kvert/Kleg were calculated from the maximal vertical ground reaction force during contact, running velocity, contact time, flight time, height, and body mass (Morin et al. 2005).
RESULTS:
There was a significant negative correlation between Kvert (102.3 ± 18.6 kN·m−1) and QF CSA (4.64 ± 0.34 cm2/kg2/3) (r = −0.593, P = 0.020), while no significant correlation between Kleg (14.7 ± 2.9 kN·m−1) and QF CSA (P > 0.05). HM (2.10 ± 0.14 cm2/kg2/3) and AD (1.89 ± 0.29 cm2/kg2/3) CSAs did not significantly correlate with Kvert/Kleg (P > 0.05).
CONCLUSION:
These results suggest that the QF is greatly hypertrophied in distance runners who do not use the elastic energy of the legs well during running. Coaching and/or training strategies to improve Kvert/Kleg during running may be useful to improve running economy, which may ultimately lead to smaller QF size.
REFERENCES:
Ando et al. (2022). J Hum Kineti, 81:65–72
Li et al. (2019). J Strength Cond Res, 35(6):1491–1499
Morin JB et al. (2005). J Appl Biomech, 21(2):167–180
Zhang et al. (2022). Front Physiol, 13:940761