Longer Ground Contact Time Is Related to a Superior Running Economy in Highly Trained Distance Runners.

ABSTRACT: Tanji, F, Ohnuma, H, Ando, R, Yamanaka, R, Ikeda, T, and Suzuki, Y. Longer ground contact time is related to a superior running economy in highly trained distance runners. J Strength Cond Res 38(5): 985-990, 2024-Running economy is a key component of distance running performance and is associated with gait parameters. However, there is no consensus of the link between the running economy (RE), ground contact time, and footstrike patterns. Thus, this study aimed to clarify the relationship between RE, ground contact time, and thigh muscle cross-sectional area (CSA) in highly trained distance runners and to compare these parameters between 2 habitual footstrike patterns (midfoot vs. rearfoot). Seventeen male distance runners ran on a treadmill to measure RE and gait parameters. We collected the CSAs of the right thigh muscle using a magnetic resonance imaging scanner. The RE had a significant negative relationship with distance running performance ( r = -0.50) and ground contact time ( r = -0.51). The ground contact time had a significant negative relationship with the normalized CSAs of the vastus lateralis muscle ( r = -0.60) and hamstrings ( r = -0.54). No significant differences were found in RE, ground contact time, or normalized CSAs of muscles between midfoot ( n = 10) and rearfoot ( n = 7) strikers. These results suggest that large CSAs of knee extensor muscles results in short ground contact time and worse RE. The effects of the footstrike pattern on the RE appear insignificant, and the preferred footstrike pattern can be recommended for running in highly trained runners.

Measuring Muscle Activity in Sprinters Using T2-Weighted Magnetic Resonance Imaging.

PURPOSE: This study aimed to investigate the level of muscle activity during sprint running using T2-weighted magnetic resonance imaging. METHODS: Fourteen male sprinters (age 21.2 [4.0] y; height 171.8 [4.2] cm, weight 65.5 [5.3] kg, 100-m personal record 11.01 [0.41] s; mean [SD]) performed 3 sets of three 60-m round-trip sprints. Before and after the round-trip sprints, 3 T magnetic resonance imaging scans were performed to obtain the T2 values of the 14 athletes' lower-extremity muscles. RESULTS: After the 60-m round-trip sprints, the T2 value of the gluteus maximus, long head of biceps femoris, semitendinosus, semimembranosus, adductor brevis, adductor longus, adductor magnus, and gracilis increased significantly. The rate of change in the T2 values before and after the 60-m round-trip sprints was notably higher in the semitendinosus and gluteus maximus than in the other muscles. CONCLUSIONS: These findings demonstrate the specific physiological metabolism of the lower-extremity muscles during fast sprinting. There are particularly high levels of muscle activity in the gluteus maximus and semitendinosus during sprint performance.

Thigh Muscularity and Sprinting Performance of National-Level Long-Distance Runners.

Long-distance runners require aerobic capacity as well as sprinting ability for superior performance; however, the factors which determine the sprinting ability of long-distance runners remain undetermined. Therefore, the purpose of our study was to examine the association between thigh muscle size and sprinting ability in national-level male long-distance runners. Nineteen male long-distance runners with 5000 m personal-best times of 13:12.63-14:14.87 participated in this study, and transaxial images of their right thighs were collected using magnetic resonance imaging. The cross-sectional areas of the quadriceps femoris, hamstrings, and adductor muscles were calculated from the transaxial images at 30%, 50%, and 70% of the distance from the greater trochanter to the lower edge of the femur; these areas were normalized by body mass. Sprint times for 100 m and 400 m were recorded on an all-weather track. The results revealed positive correlations between the normalized cross-sectional areas of the quadriceps femoris at 50% and 70% of the thigh length and the 100 m (r = 0.666, p = 0.002 and r = 0.531, p = 0.019, respectively) and 400 m sprint times (r = 0.769, p < 0.001 and r = 0.580, p = 0.009, respectively); hence, the larger the quadriceps, the slower the sprint speed. However, no association was found between the normalized cross-sectional areas of the hamstrings or adductor muscles and sprinting performance. Therefore, running motions which activate the quadriceps femoris much more than the hamstrings and adductor muscles should be avoided by national-level long-distance runners.

Augmented muscle glycogen utilization following a single session of sprint training in hypoxia.

PURPOSE: This study determined the effect of a single session of sprint interval training in hypoxia on muscle glycogen content among athletes. METHODS: Ten male college track and field sprinters (mean ± standard error of the mean: age, 21.1 ± 0.2 years; height, 177 ± 2 cm; body weight, 67 ± 2 kg) performed two exercise trials under either hypoxia [HYPO; fraction of inspired oxygen (FiO2), 14.5%] or normoxia (NOR: FiO2, 20.9%). The exercise consisted of 3 × 30 s maximal cycle sprints with 8-min rest periods between sets. Before and immediately after the exercise, the muscle glycogen content was measured using carbon magnetic resonance spectroscopy in vastus lateralis and vastus intermedius muscles. Moreover, power output, blood lactate concentrations, metabolic responses (respiratory oxygen uptake and carbon dioxide output), and muscle oxygenation were evaluated. RESULTS: Exercise significantly decreased muscle glycogen content in both trials (interaction, P = 0.03; main effect for time, P < 0.01). Relative changes in muscle glycogen content following exercise were significantly higher in the HYPO trial (- 43.5 ± 0.4%) than in the NOR trial (- 34.0 ± 0.3%; P < 0.01). The mean power output did not significantly differ between the two trials (P = 0.80). The blood lactate concentration after exercise was not significantly different between trials (P = 0.31). CONCLUSION: A single session of sprint interval training (3 × 30 s sprints) in hypoxia caused a greater decrease in muscle glycogen content compared with the same exercise under normoxia without interfering with the power output.

Effect of inspiratory resistive training on diaphragm shear modulus and accessory inspiratory muscle activation.

This study aimed to elucidate changes in diaphragm and accessory inspiratory muscle (sternocleidomastoid (SCM) muscle and intercostal muscle (IC)) function after a 6-week training program. Nineteen male elite collegiate swimmers were assigned to either a control group (n = 9) or training group (n = 10). The subjects in the training group performed 30 maximum inspirations at a load resistance of 50% of maximum inspiratory mouth pressure (PImax) using an inspiratory muscle training device. These were conducted twice per day and 6 days per week. At baseline and after 6 weeks, PImax, shear modulus of the diaphragm, and electromyograms (EMG) of the SCM and IC during a maximal inspiratory maneuver were evaluated. Relative change in PImax was greater in the training group than in controls. The shear modulus during a PImax maneuver had increased significantly in both groups after 6 weeks. EMG amplitudes of the SCM increased in the training group after 6 weeks, but not in the control group. EMG amplitudes of the IC did not change after 6 weeks in either group. These results suggest that 6-week inspiratory resistive training significantly improves the activation of the SCM, which could be one of the major mechanisms behind increases in inspiratory muscle strength after resistive training. Novelty Six-week inspiratory resistive training increased diaphragm stiffness during maximal inspiration maneuver. Six-week inspiratory resistive training increased electromyogram amplitudes of the sternocleidomastoid during maximal inspiration maneuver.

Sprinting Ability as an Important Indicator of Performance in Elite Long-Distance Runners.

PURPOSE: Increases in maximal oxygen uptake (V˙O2max) and running economy improve performance in long-distance runners. Nevertheless, long-distance runners require sprinting ability to win, especially in the final phase of competitions. The authors determined the relationships between performance and sprinting ability, as well as other abilities in elite long-distance runners. METHODS: The subjects were 12 elite long-distance runners. Mean official seasonal best times in 5000-m (5000 m-SB) and 10,000-m (10,000 m-SB) races within 1 year before or after the examination were 13:58.5 (0:18.7) and 28:37.9 (0:25.2) (mean [SD]), respectively. The authors measured 100-m and 400-m sprint times as the index of sprinting ability. They also measured V˙O2max and running economy (V˙O2 at 300 m·min-1 of running velocity). They used a single correlation analysis to assess relationships between 5000 m-SB or 10,000 m-SB and other elements. RESULTS: There were significant correlations between 5000 m-SB was significantly correlated with 100-m sprint time (13.3 [0.7] s; r = .68, P = .014), 400-m sprint time (56.6 [2.7] s; r = .69, P = .013), and running economy (55.5 [3.9] mL·kg-1·min-1; r = .59, P = .045). There were significant correlations between 10,000 m-SB and 100-m sprint time (r = .72, P = .009) and 400-m sprint time (r = .85, P < .001). However, there was no significant correlation between 5000 m-SB or 10,000 m-SB and V˙O2max (72.0 [3.8] mL·kg-1·min-1). CONCLUSIONS: The authors' data suggest that sprinting ability is an important indicator of performance in elite long-distance runners.

How to Maintain Maximal Straight Path Running Speed on a Curved Path in Sprint Events.

This study aims to clarify the ideal technique for running on a curved path during sprinting events. Participants were twelve male track and field athletes including long jumpers and sprinters. The participants performed a 60-m sprint with maximal effort on straight and curved paths. Participants were divided into "good curve runners" and "poor curve runners" according to the curved path running speed relative to that of the straight path. Kinematic variables and ground reaction forces (GRFs) were registered and compared between the groups and paths. The running speed, step length, and flight distance of the outside leg on the curved path were lower than on the straight path only in poor curve runners. The medial-lateral GRF and impulse showed an increase during curved path running for both groups. However, the maximum posterior GRF and impulse decreased only in poor curve runners. The ideal technique for running on a curved path is to maintain the same kinematics and kinetics in the sagittal plane as on a straight path.

Hyperoxia Extends Time to Exhaustion During High-Intensity Intermittent Exercise: a Randomized, Crossover Study in Male Cyclists.

BACKGROUND: Some endurance athletes exhibit exercise-induced arterial hypoxemia during high-intensity exercise. Inhalation of hyperoxic gas during exercise has been shown to counteract this exercise-associated reduction in hemoglobin oxygen saturation (SaO2), but the effects of hyperoxic gas inhalation on performance and SaO2 during high-intensity intermittent exercise remain unclear. This study investigated the effects of hyperoxic gas inhalation on performance and SaO2 during high-intensity intermittent cycling exercise. METHODS: Eight male cyclists performed identical intermittent exercise tests (five sets of 3-min high-intensity cycling alternated with 3-min active recovery periods) under two different inspired air conditions, hyperoxia (HO; FIO2 = 0.36) and normoxia (NO; FIO2 = 0.21). The fifth set of each test was terminated at exhaustion, and the exercise time to exhaustion was recorded. Variables associated with arterial oxygen saturation (SpO2) were measured using an ear pulse oximeter. RESULTS: Time to exhaustion under HO conditions was significantly longer than under NO conditions (34.9 ± 4.6 vs. 30.0 ± 2.5 min, P = 0.004, ES = 1.32). SpO2 was maintained under HO conditions but decreased under NO conditions. CONCLUSIONS: Hyperoxic gas inhalation during the entire high-intensity intermittent exercise enhanced exercise performance in male cyclists.