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.

DMD transcripts in CRL-2061 rhabdomyosarcoma cells show high levels of intron retention by intron-specific PCR amplification.

BACKGROUND: The DMD gene encoding dystrophin is mutated in Duchenne muscular dystrophy, a fatal progressive muscle wasting disease. DMD has also been shown to act as a tumor suppressor gene. Rhabdomyosarcoma (RMS) is a mesodermal sarcoma that shares characteristics of skeletal muscle precursors. Products of the DMD gene in RMS have not yet been fully clarified. Here, DMD products were analyzed in CRL-2061 cells established from alveolar RMS. METHODS: The 14-kb long DMD cDNA was PCR amplified as 20 separated fragments, as were nine short intron regions. Dystrophin was analyzed by Western blotting using an antibody against the C-terminal region of dystrophin. RESULTS: Sixteen of the 20 DMD cDNA fragments could be amplified from CRL-2061 cells as muscle cDNA. Three fragments included aberrant gene products, including one in which exon 71 was omitted and one each with retention of introns 40 and 58. In one fragment, extending from exon 70 to 79, no normally spliced product was obtained. Rather, six alternatively spliced products were identified, including a new product deleting exon 73, with the most abundant product showing deletion of exon 78. Although dystrophin expression was expected in CRL-2061 cells, western blotting of cell lysates showed no evidence of dystrophin, suggesting that translation of full-length DMD mRNA was inhibited by intron retention that generated a premature stop codon. Intron specific PCR amplification of nine short introns, showed retention of introns 40, 58, and 70, which constituted about 60, 25 and 9%, respectively, of the total PCR amplified products. The most abundant DMD transcript contained two abnormalities, intron 40 retention and exon 78 skipping. CONCLUSIONS: Intron-specific PCR amplification showed that DMD transcripts contained high levels of introns 40, 58 and 70. Retention of these introns may have been responsible for the lack of dystrophin expression by CRL-2061 cells, thereby abolishing the tumor suppressor activity of dystrophin.

Relationship between motor corticospinal excitability and ventilatory response during intense exercise.

PURPOSE: Effort sense has been suggested to be involved in the hyperventilatory response during intense exercise (IE). However, the mechanism by which effort sense induces an increase in ventilation during IE has not been fully elucidated. The aim of this study was to determine the relationship between effort-mediated ventilatory response and corticospinal excitability of lower limb muscle during IE. METHODS: Eight subjects performed 3 min of cycling exercise at 75-85 % of maximum workload twice (IE1st and IE2nd). IE2nd was performed after 60 min of resting recovery following 45 min of submaximal cycling exercise at the workload corresponding to ventilatory threshold. Vastus lateralis muscle response to transcranial magnetic stimulation of the motor cortex (motor evoked potentials, MEPs), effort sense of legs (ESL, Borg 0-10 scale), and ventilatory response were measured during the two IEs. RESULTS: The slope of ventilation (l/min) against CO2 output (l/min) during IE2nd (28.0 ± 5.6) was significantly greater than that (25.1 ± 5.5) during IE1st. Mean ESL during IE was significantly higher in IE2nd (5.25 ± 0.89) than in IE1st (4.67 ± 0.62). Mean MEP (normalized to maximal M-wave) during IE was significantly lower in IE2nd (66 ± 22 %) than in IE1st (77 ± 24 %). The difference in mean ESL between the two IEs was significantly (p < 0.05, r = -0.82) correlated with the difference in mean MEP between the two IEs. CONCLUSIONS: The findings suggest that effort-mediated hyperventilatory response to IE may be associated with a decrease in corticospinal excitability of exercising muscle.

The 400- and 800-m Track Running Induces Inspiratory Muscle Fatigue in Trained Female Middle-Distance Runners.

Inspiratory muscle fatigue (IMF) may limit exercise performance. A few studies have reported that IMF occurs after short-duration swimming exercise, but whether short-duration running can induce IMF remains unclear. Intra-abdominal pressure is increased during running through diaphragmatic activation to stabilize the spine during movements of the upper limbs. This occurs along with the increased inspiratory muscle effort associated with increased respirations during exercise; thus, we hypothesized that short-duration running exercise would induce IMF. To test this hypothesis, we measured maximal inspiratory pressure (MIP) before and after 400- and 800-m track running sessions. Eight female middle-distance (400, 800 m) runners performed a 400- and 800-m running test. Maximal inspiratory pressure was measured before and after each test using a portable autospirometer. The mean MIPs were significantly lower after running than before running; values obtained were 107 ± 25 vs. 97 ± 27 cmH2O (p = 0.01, effect size [ES] = 0.65) and 108 ± 26 vs. 92 ± 27 cmH2O (p = 0.01, ES = 0.74) before vs. after the 400- and 800-m tests, respectively. The mean MIP after the 800-m test was significantly lower than after the 400-m test (p = 0.04, ES = 0.48). There was no correlation between IMF value and running time (r = 0.53 and r = -0.28 for either the 400- and 800-m tests, respectively; p > 0.05). In conclusion, IMF occurs after short-duration running exercise. Coaches could consider prescribing inspiratory muscle training or warm-up in an effort to reduce the inevitable IMF associated with maximal effort running.

Tissue distribution of renadirsen sodium, a dystrophin exon-skipping antisense oligonucleotide, in heart and diaphragm after subcutaneous administration to cynomolgus monkeys.

The pharmacokinetics and tissue distribution of renadirsen sodium, a dystrophin exon-skipping phosphorothioate-modified antisense oligonucleotide with 2'-O,4'-C-ethylene-bridged nucleic acid (ENA), after subcutaneous or intravenous administration to cynomolgus monkeys were investigated. The plasma concentration of renadirsen after subcutaneous administration at 1, 3, and 10 mg/kg increased with the dose. The absolute bioavailability at 3 mg/kg after subcutaneous administration was calculated as 88.6%, and the time to reach maximum plasma concentration of renadirsen was within 4 h, indicating the efficient and rapid absorption following subcutaneous administration. The exposure of muscle tissues to renadirsen was found to increase with repeated dosing at 6 mg/kg, and higher exposure was observed in the diaphragm and heart than in the quadriceps femoris and anterior tibialis muscles. Renadirsen achieved more exon 45-skipped dystrophin mRNA in the diaphragm and heart than in the quadriceps femoris and anterior tibialis muscles. Renadirsen also showed a cumulative skipping effect in a repeated-dose study. The findings on exon 45-skipped dystrophin mRNA in these muscle tissues were consistent with the concentration of renadirsen in these tissues. Because it is not feasible to directly evaluate drug concentration and exon skipping in the heart and diaphragm in humans, the pharmacokinetics and pharmacodynamics of renadirsen in these tissues in monkeys are crucial for the design and interpretation of clinical settings.

Relationship between effort sense and ventilatory response to intense exercise performed with reduced muscle glycogen.

The purpose of the present study was to examine the effects of muscle glycogen reduction on surface electromyogram (EMG) activity and effort sense and ventilatory responses to intense exercise (IE). Eight subjects performed an IE test in which IE [100-105% of peak O(2) uptake ([Formula: see text]), 2 min] was repeated three times (IE(1st), IE(2nd) and IE(3rd)) at 100-120-min intervals. Each interval consisted of 20-min passive recovery, 40-min submaximal exercise at ventilatory threshold intensity (51.5 ± 2.7% of [Formula: see text]), and a further resting recovery for 40-60 min. Blood pH during IE and subsequent 20-min recovery was significantly higher in the IE(3rd) than in the IE(1st) (P < 0.05). Effort sense of legs during IE was significantly higher in the IE(3rd) than in the IE(1st) and IE(2nd). Integrated EMG (IEMG) measured in the vastus lateralis during IE was significantly lower in the IE(3rd) than in the IE(1st). In contrast, mean power frequency of the EMG was significantly higher in the IE(2nd) and the IE(3rd) than in the IE(1st). Ventilation ([Formula: see text]) in the IE(3rd) was significantly higher than that in the IE(1st) during IE and the first 60 s after the end of IE. These results suggest that ventilatory response to IE is independent of metabolic acidosis and at least partly associated with effort sense elicited by recruitment of type II fibers.

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.

Effects of sodium bicarbonate ingestion on EMG, effort sense and ventilatory response during intense exercise and subsequent active recovery.

To determine whether post-exercise ventilation is related to decrease in blood pH and also whether post-exercise ventilation, associated or not with decreased blood pH, involves an increase in central motor command during exercise, we examined the effects of NaHCO(3) ingestion on the ventilatory response ([Formula: see text]E), integrated electromyogram (iEMG) and effort sense of legs (ESL) during intense exercise (IE) and subsequent active recovery. Subjects performed two IE tests (105-110% of maximal work rate, 2 min) after ingestion of NaHCO(3) or CaCO(3). Subjects performed light load exercise (20 W) before and after IE for 6 min and 30 min, respectively. Although there was a significant difference in blood pH between the two conditions during and after IE, [Formula: see text]E, iEMG and ESL were similar. iEMG returned to the pre-IE level immediately after the end of IE, while ESL showed slow recovery. [Formula: see text]E decreased rapidly until about 50 s after the end of IE (fast phase) and then showed a slow recovery kinetics (slow phase). The ventilatory responses during the fast phase and during the slow phase were correlated with ESL at the end of IE and from 3 min after the end of IE, respectively. Moreover, there was no significant difference in the slopes and intercepts of regression lines between [Formula: see text]E and ESL under the two conditions in both phases. These results suggest that the ventilatory response after IE is associated with effort sense indirectly-elicited by central motor command, but the effort sense-mediated response is not affected by blood pH.

Ventilatory response to moderate incremental exercise performed 24 h after resistance exercise with concentric and eccentric contractions.

In order to test our hypothesis that muscle condition has an effect on the cognition of self-motion and consequently on the ventilatory response during exercise, six healthy subjects performed a moderate incremental exercise test (IET) on a cycle ergometer under two conditions [resistance exercise condition (REC) and control condition (CC)]. In the REC, resistance exercise (30 incline leg presses) was conducted during two sessions scheduled at 48 and then 24 h prior to the IET. For the CC, the subjects were instructed to refrain from participating in strenuous exercise for a period of 2 days prior to the IET. In the IET, the workload was increased from 78 to 118 watts in steps of 8 watts every 3 min. Although the ventilatory response during the IET was significantly higher in the REC than in the CC, there were no significant differences in cognitive indexes (RPE and awareness of change in workload) between the two conditions. In addition, the magnitude of muscle soreness was significantly higher in the REC than in the CC. However, the level of soreness in the REC was very low, and there were no significant differences in blood lactate concentration and integrated EMG between the two conditions. These results suggest that a change in peripheral neural reflex is the primary cause of increased ventilatory response to moderate exercise after resistance exercise, although the role of a cognitive element cannot be absolutely excluded.

Effect of Resistance Training of Psoas Major in Combination With Regular Running Training on Performance in Long-Distance Runners.

PURPOSE: The study determined whether the increase in the cross-sectional area (CSA) of psoas major, which is known as a hip-flexion muscle, by resistance training combined with running training improves the performance of long-distance runners. METHODS: Subjects were 8 well-trained male long-distance runners. The personal best time in a 5000-m race was 15:10.0 (0:20.5) (mean [SD]). Each subject performed resistance training twice per week with running training for 12 weeks. The authors used 3 resistance training regimens that would train the hip flexor muscles. Training intensity was a maximum of 10 repetitions. The training amount was 3 sets × 10 times during the first 4 weeks followed by 4 sets × 10 times during the last 8 weeks. The authors measured the CSA of psoas major using magnetic resonance imaging and the performance of long-distance runners using a constant velocity running test before (pre) and after (post) the training term. RESULTS: The combination training significantly (P < .01, d = 0.34) increased the CSA of psoas major (pre: 16.2 [1.5] cm2, post: 16.7 [1.4] cm2) and significantly (P < .01, d = 1.41) improved the duration of the constant velocity running test (pre: 500 [108] s, post: 715 [186] s). Moreover, multiple regression analysis showed that the pre to post change in the duration of the constant velocity exercise was significantly correlated with the change in CSA of the psoas major. CONCLUSION: The authors suggest that resistance training of psoas major with running training is correlated with an improvement in the performance of long-distance runners.

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.

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.