Author(s): TANJI, F., NISHIDE, N., MOROZUMI, H., MIYAZAKI, S., Institution: TOKAI UNIVERSITY, Country: JAPAN, Abstract-ID: 686

INTRODUCTION:
Ground contact time during running is less than 250 ms and becomes shorter as speed increases. Distance runners must produce force to support body weight from their lower limb muscles in this short ground contact time. The short contraction time may not allow for maximal muscle force. However, the ability to produce faster and higher lower limb muscle force would contribute to increased running gait stability and less energy expenditure (i.e., increased running economy [RE]) at a given running speed. The use of isometric mid-thigh pull (IMTP) can be used to measure the lower limb’s maximum force-generating capability (peak force), the rate at which force is developed (rate of force development [RFD]) and force produced at various time points (force epoch) (Lum et al., 2020). Therefore, we aimed to clarify the relationship between force-time characteristics obtained from IMTP and running economy (RE) at low and high running speeds.
METHODS:
Twenty-five well-trained male distance runners (age, 19 ± 1 years; height: 172.6 ± 4.5 cm, body mass: 57.3 ± 3.6 kg), with a mean seasonal best time of 14:07.8 ± 0:54.7 for 5,000 m run, participated in this study. They performed a multi-intermittent incremental running test on a treadmill. RE was calculated using oxygen uptake, respiratory exchange ratio and accumulated blood lactate concentration (Tanji et al., 2017) at 250 and 330 m/min running (their blood lactate concentration was 1.8 ± 0.3 and 5.3 ± 1.3 mmol/L, respectively). In addition, they performed an IMTP test on an instrumented force platform with an IMTP testing rack. The highest absolute peak force and RFD at 0−100 (RFD0−100) and 0−200 ms (RFD0−200) from the onset of pull were used for analysis. Pearson’s correlation coefficient was analyzed to determine the association between IMTP measures and RE, and the significance was set at a P value of < 0.05.
RESULTS:
The absolute peak force, RFD0−100 and RFD0−200 were 1722 ± 255 N, 5405 ± 1788 N/s and 4124 ± 919 N/s, respectively. There was no significant relationship between RE at 250 m/min (0.98 ± 0.06 kcal/kg/km) and each IMTP measure (r = −0.14, −0.09 and −0.13, respectively; P > 0.05). RE at 330 m/min (1.09 ± 0.08 kcal/kg/km) had a significant relationship with the RFD0−200 (r = −0.46; P < 0.05) and no significant relationship with the absolute peak force and RFD0−100 (r = −0.31 and −0.28, respectively; P > 0.05).
CONCLUSION:
These results suggest that the ability to produce high force up to 200 ms in lower limb strength contributes to superior RE at high running speed. It can be concluded that well-trained distance runners must train their lower limb muscle strength and run-based training.
REFERENCES: Lum D et al. (2020) J Trainology, 9(2): 54−59; Tanji F et al. (2017) J Phys Fitness Sports Med 6: 41−48.
CONTACT: fumiya.tanji@tsc.u-tokai.ac.jp