ECSS Paris 2023: CP-BM06
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
Read CV Ryosuke AndoECSS Paris 2023: CP-BM06
INTRODUCTION: Elastic band resistance training (EBRT) is beneficial for improving the specific strengths of sprinters(1). However, it is not clear whether the mode and working characteristics of the swinging leg muscle exertion while using swing technique are consistent with those during actual sprint performance. To achieve the optimal training effect, those specific strengths must be trained by using training methods that are specific to, and meet, or exceed the requirements of competitive contexts(2). In other words, the training effect of those specific strengths can be greatly affected by training regimens including motion range, movement speed, muscle exertion characteristics, working mode, and the extent to which the energy supply systems adapt to the requirements of specific movements and techniques(3). Therefore, the study aimed to use the synchronous testing methods of kinematics and sEMG to test the swing technique action in maximum sprint running(MSR) and the swing technique during the EBRT for Chinese elite sprinters. In addition, the study also explored the muscle sEMG characteristics of the swing leg in these athletes’ response to sprint performance and specific strength training. METHODS: Surface electromyography telemetry technology and high-speed camera were used to simultaneously test kinematics and muscle exertion characteristics of lower limb swing technique in high-level sprinters during EBRTand MSR. RESULTS: The angle changes response to swing technique showed a significant difference in Maximum value of thigh angle(EBRT:183 ± 4,MSR:161±6,Deg;p=0.000), thigh flexion range(EBRT:160±9,MSR:99±6,Deg;p=0.000), and minimum value of knee angle(EBRT:40 ± 11, MSR: 30 ± 3, Deg;p=0.048) between EBRT and MSR . However, no significant difference was shown in the values for knee flexion range(EBRT:110 ± 22,MSR :122 ±7,Deg;p=0.186). The angular velocity changes response to swing technique showed a significant higher for maximum value of thigh flexion angular velocity in EBRT than MSR (EBRT:1069 ± 168, MSR: 828 ±72 , deg•s-1;p=0.016). When completing EBRT and MSR swing technique, each muscle group of the swing leg show distinct temporal sequence. The standardized mean value of Average EMG (AEMG) of FL(p=0.000) and SEM(P= 0.008 )were shown in significant difference between EBRT and MSR.there was a significant difference in AEMG of RF(p=0.087), GM(p=0.012) ,TA(p=0.472) between EBRT and MSR . No significant difference was shown in AEMG of VMO(p=0.080),VLO(p=0.055),BF(p=0.187), Ta(p=0.472),LG(P=0.562) between EBRT and MSR. CONCLUSION: In the practice of special strength training for sprinting running, we should know EBRT could effectively develop thigh forward swing speed and develop the special strength of single muscle groups such as RFandTA; however, the leg muscle activity sequence and muscle group coordination were not consistent with MSR swing technique. This may affect the training effect of the specific strengths of lower limb swing technique for optimal sprint performance.
Read CV Zhang JieECSS Paris 2023: CP-BM06
INTRODUCTION: The towing sprint is one of the assisted sprinting training methods. It can increase sprinting speed due to improved step frequency and step length1),2). Consequently, the kinematics and kinetics of assisted sprinting differ from normal sprinting, including shorter contact time2), smaller knee angle change during stance phase3), and larger impulse4). Therefore, assisted sprinting improves sprint velocity by altering the kinematics of lower leg and resultant force. However, most of the previous research has compared assisted sprinting with normal sprinting, leaving the acute effects of assisted sprinting on subsequent sprint performance unexplored. Hence, this study aimed to determine the acute effect of assisted sprinting on kinematics and kinetics of subsequent sprinting. METHODS: Nineteen male sprinters (age: 20.0 ± 1.7 years, height: 1.74 ± 0.06 m, weight: 66.0 ± 4.8 kg, world athletics score: 883.6 ± 96.2 score) performed maximal sprinting. Each sprinting sequence involved three trials: two unassisted 60-m sprinting before and after a single assisted sprinting using a motorized towing device with a 10% body weight load in isotonic mode. The sprinting motion from 50 to 60-m was recorded using two video cameras (240 fps). Sprinting speed, spatiotemporal and kinematic variables were calculated from the captured video in the sagittal plane. Plantar loading in the forefoot, midfoot, rearfoot and their total loading during sprinting were recorded using wireless, mobile insole sensor. Peak plantar loading and impulse during stance phase were calculated. RESULTS: No significant differences were found in sprinting speed and spatiotemporal variables between Pre and Post. However, the mean values of hip flexion and extension angular velocities during the flight phase were significantly higher in the Post compared to the Pre (hip flexion: Pre 370.92 ± 38.20 deg/s, Post 405.41 ± 42.27 deg/s, hip extension: Pre 363.96 ± 35.88 deg/s, Post 389.60 ± 31.14 deg/s). Both peak total plantar loading and impulse were higher in the Post compared to the Pre, particularly in the rearfoot, although no significant differences were observed in plantar loading. CONCLUSION: Sprinting speed was not significantly increased following the assisted sprinting, although the acute effect of increasing the thigh swinging velocity was observed. 【References】 1) Mero & Komi, Eur J Appl Physiol, 1986. 2) Clark et al., J Strength Cond Res, 2021. 3) Sugiura & Aoki, Advances in exercise and sports physiology, 2008. 4) Mero et al., Int J Sports Med, 1987.
Read CV Yohei YamazakiECSS Paris 2023: CP-BM06