Alteration in neuromuscular function after a 5 km running time trial

The aim of this study was to characterize the effect of a 5 km running time trial on the neuromuscular properties of the plantar flexors. Eleven well-trained triathletes performed a series of neuromuscular tests before and immediately after the run on a 200 m indoor track. Muscle activation (twitch interpolation) and normalized EMG activity were assessed during maximal voluntary contraction (MVC) of plantar flexors. Maximal soleus H-reflexes and M-waves were evoked at rest (i.e. H (MAX) and M (MAX), respectively) and during MVC (i.e. H (SUP) and M (SUP), respectively). MVC significantly declined (-27%; P < 0.001) after the run, due to decrease in muscle activation (-8%; P < 0.05) and M (MAX)-normalized EMG activity (-13%; P < 0.05). Significant reductions in M-wave amplitudes (M (MAX): -13% and M (SUP): -16%; P < 0.05) as well as H (MAX)/M (MAX) (-37%; P < 0.01) and H (SUP)/M (SUP) (-25%; P < 0.05) ratios occurred with fatigue. Following exercise, the single twitch was characterized by lower peak torque (-16%; P < 0.001) as well as shorter contraction (-19%; P < 0.001) and half-relaxation (-24%; P < 0.001) times. In conclusion, the reduction in plantar flexors strength induced by a 5 km running time trial is caused by peripheral adjustments, which are attributable to a failure of the neuromuscular transmission and excitation-contraction coupling. Fatigue also decreased the magnitude of efferent motor outflow from spinal motor neurons to the plantar flexors and part of this suboptimal neural drive is the result of an inhibition of soleus motoneuron pool reflex excitability.     

The optimal locomotion on gradients: walking,running or cycling?

On level ground, cycling is more economical than running, which in turn is more economical than walking in the high speed range. This paper investigates whether this ranking still holds when moving on a gradient, where the three modes are expected to be mainly facing the same burden, i.e. to counter gravity. By using data from the literature we have built a theoretical framework to predict the optimal mode as a function of the gradient. Cycling was found to be the mode of choice only below 10–15% gradient, while above it walking was the least expensive locomotion type. Seven amateur bikers were then asked to walk, run and ride on a treadmill at different gradients. The speed was set so as to maintain almost constant the metabolic demand across the different gradients. The results indicate that the "critical slope", i.e. the one above which walking is less expensive than cycling (and running), is about 13–15%. One subject was loaded during bipedal gaits with a bicycle-equivalent mass, to simulate to cross-country cycling situation. The critical slope was close to 20%, due to the higher metabolic cost of loaded walking and running. Part of the findings can be explained by the mechanically different paradigms of the three locomotion types.     

Are there differences in running economy at different velocities for well-trained distance runners?

The present study investigated whether there are differences in running economy at different velocities for well-trained distance runners, and to what extent a commonly used incremental protocol for measuring oxygen uptake (VO₂) at different velocities affects the reliability of these measurements. Fifteen well-trained distance runners (9 male and 6 female) participated in this study. Gross oxygen cost of running (C _R), heart rate (HR) and [La⁻]_b during 5-min runs at velocities ranging from 8.0 to 17 km h⁻¹, representing intensities ranging from 60 to 90% of maximal oxygen consumption (VO_2max) was measured on two different days in random order. The athletes were also tested for lactate threshold, VO_2max and time to exhaustion at MAS (_tMAS). No significant differences in C _R between the different relative velocities or the different set velocities were found up to 90% of VO_2max. The incremental protocol for measuring VO₂ at different velocities was found not to affect the reliability of these measurements. All athletes reached their VO_2max whilst running to exhaustion at MAS. The females showed significantly lower VO_2max, but significantly better C _R than the males. At velocities representing intensities between 60 and 90% of VO_2max, no differences in C _R were found. The commonly used incremental protocol for measuring oxygen uptake (VO₂) at different velocities was found not to affect the reliability of these measurements. This means that C _R measured at sub-maximal velocities are representative for C _R at race velocity for distances above 10,000 m for most runners.     

Estimation of %V˙O2 reserve from heart rate during arm exercise and running

The purpose of the present investigation was to examine the relationship between the percent heart rate reserve (%HRR) in arm exercise and the corresponding percent oxygen uptake (V˙O₂) reserve, and to compare this relationship to that occurring in running. Fourteen male physical education students took part in the study. Each subject performed a maximal running exercise test and a maximal arm cycling test. The subjects also performed three submaximal exercise bouts (in both exercise modes) at 30%, 60% and 80% of their HRR. The subjects were monitored for their heart rate (HR) at rest, maximal HR (HR_max), HR at submaximal work loads, maximal V˙O₂ (V˙O_2max), V˙O₂ at rest and V˙O₂ at submaximal loads. For each subject, load and exercise mode, %HRR and %V˙O₂ reserve were calculated (from HR_max and V˙O_2max as measured during running and arm cycling) and the relationship between the two was evaluated. The main finding of the present investigation is that the prediction of %V˙O₂ reserve in arm cycling from %HRR is grossly overestimated when calculated from HR_max and V˙O_2max measured during running. The prediction is better but still overestimated when calculated from HR_max and V˙O_2max measured during arm cycling. The findings indicate a better prediction of %V˙O₂ reserve from %HRR for running than for arm exercise. These findings should be taken into consideration when prescribing the target HR for arm training. Accepted: 24 July 2000     

A single test for the determination of parameters of the speed–time relationship for running

A validated expeditious method is needed to determine critical speed (CS) and the finite distance that can be covered above CS (D′). We tested the hypothesis that a single all-out 3-min running test would accurately determine CS and D′. Seven healthy subjects completed three constant-speed runs on a treadmill for the determination of CS and D′, as well as an all-out 3-min test on a track for the determination of end-test speed (ES) and the distance above end-test speed (DES). ES (13.4 ± 2.8 km h⁻¹) was not significantly different from the speed-1/time model CS (13.3 ± 2.8 km h⁻¹). While DES (141 ± 34 m) was not significantly different from D′ (204 ± 103 m), it underestimated D′ in 5 of 7 subjects. Thus, the speed-1/time model CS can be accurately determined using a single 3-min test, while caution should be used in relating DES to D′.     

Influence of the world’s most challenging mountain ultra-marathon on energy cost and running mechanics

Purpose

To examine the effects of the world’s most challenging mountain ultra-marathon (Tor des Géants^® 2012) on the energy cost of three types of locomotion (cycling, level and uphill running) and running kinematics.

Methods

Before (pre-) and immediately after (post-) the competition, a group of ten male experienced ultra-marathon runners performed in random order three submaximal 4-min exercise trials: cycling at a power of 1.5 W kg^?1 body mass; level running at 9 km h^?1 and uphill running at 6 km h^?1 at an inclination of +15 % on a motorized treadmill. Two video cameras recorded running mechanics at different sampling rates.

Results

Between pre- and post-, the uphill-running energy cost decreased by 13.8 % (P = 0.004); no change was noted in the energy cost of level running or cycling (NS). There was an increase in contact time (+10.3 %, P = 0.019) and duty factor (+8.1 %, P = 0.001) and a decrease in swing time (?6.4 %, P = 0.008) in the uphill-running condition.

Conclusion

After this extreme mountain ultra-marathon, the subjects modified only their uphill-running patterns for a more economical step mechanics.     

Fast-start strategy increases the time spent above 95 %VO2max during severe-intensity intermittent running exercise

This study aimed to use the intermittent critical velocity (ICV) model to individualize intermittent exercise and analyze whether a fast-start strategy could increase the time spent at or above 95 %VO_2max (t95VO_2max) during intermittent exercise. After an incremental test, seven active male subjects performed three intermittent exercise tests until exhaustion at 100, 110, and 120 % of the maximal aerobic velocity to determine ICV. On three occasions, the subjects performed an intermittent exercise test until exhaustion at 105 % (IE₁₀₅) and 125 % (IE₁₂₅) of ICV, and at a speed that was initially set at 125 %ICV but which then decreased to 105 %ICV (IE_125–105). The intermittent exercise consisted of repeated 30-s runs alternated with 15-s passive rest intervals. There was no difference between the predicted and actual Tlim for IE₁₂₅ (300 ± 72 s and 284 ± 76 s) and IE₁₀₅ (1,438 ± 423 s and 1,439 ± 518 s), but for IE_125–105 the predicted Tlim underestimated the actual Tlim (888 ± 211 s and 1,051 ± 153 s, respectively). The t95VO_2max during IE_125–105 (289 ± 150 s) was significantly higher than IE₁₂₅ (113 ± 40 s) and IE₁₀₅ (106 ± 71 s), but no significant differences were found between IE₁₂₅ and IE₁₀₅. It can be concluded that predicting Tlim from the ICV model was affected by the fast-start protocol during intermittent exercise. Furthermore, fast-start protocol was able to increase the time spent at or above 95 %VO_2max during intermittent exercise above ICV despite a longer total exercise time at IE₁₀₅.     

GSK3β inhibition and LEF1 upregulation in skeletal muscle following a bout of downhill running

Canonical Wnt signaling is important in skeletal muscle repair but has not been well characterized in response to physiological stimuli. The objective of this study was to assess the effect of downhill running (DHR) on components of Wnt signaling. Young, male C57BL/J6 mice were exposed to DHR. Muscle injury and repair (MCadherin) were measured in soleus. Gene and protein expression of Wnt3a, active β-catenin, GSK3β, and LEF1 were measured in gastrocnemius. Muscle injury increased 6 days post-DHR and MCadherin protein increased 5 days post-DHR. Total and active GSK3β protein decreased 3 days (9-fold and 3.6-fold, respectively) post-DHR. LEF1 protein increased 6 days (5-fold) post-DHR. DHR decreased GSK3β and increased LEF1 protein expression, but did not affect other components of Wnt signaling. Due to their applicability, using models of physiological stimuli such as DHR will provide significant insight into cellular mechanisms within muscle.     

Acute and 2?days delayed effects of exhaustive stretch-shortening cycle exercise on barefoot walking and running patterns

This study investigated the acute and 2?days delayed influences of exhaustive stretch-shortening cycle exercise (SSC) on barefoot walking and running gait patterns. The SSC exercise was performed on a sledge apparatus, on which the subjects (N?=?10) repeated until exhaustion intermittent series of 25 bilateral submaximal rebounds. Maximal drop-jumps and submaximal barefoot treadmill walking and running were performed before (PRE) and after (POST) the exhaustive exercise and repeated 48?h (D2) later. Electromyographic activity and 3D kinematics of the right lower limb and foot were recorded for 15?s at gait initiation (BEG) and at the end (END: at 3?min of walk and 5?min of run). The exhaustive SSC exercise resulted in 6% reductions in maximal drop jump performance at POST and D2, and affected mostly both gait patterns at D2. The walking pattern presented compensatory neural adjustments within the triceps surae muscle group. This expected pain-induced protective strategy of the soleus muscle was sufficient to preserve the kinematics pattern. The running condition revealed a major knee strategy, which might support the concept of pain protective strategy of knee extensor muscles at the expense of impact cushioning. Regardless the testing session, most parameters showed fatigue-induced changes at gait initiation (BEG), which were opposite to subsequent BEG to END adjustments. This is likely to support anticipatory strategies rather than progressive adjustments during the exercise.     

V max estimate from three-parameter critical velocity models: validity and impact on 800 m running performance prediction

The purpose of this study was to evaluate the validity of maximal velocity (V _max) estimated from three-parameter systems models, and to compare the predictive value of two- and three-parameter models for the 800 m. Seventeen trained male subjects performed five randomly ordered constant velocity tests (CVT), a maximal velocity test (mean velocity over the last 10 m portion of a 40 m sprint) and a 800 m time trial (V _{800 m}). Five systems models (two three-parameter and three two-parameter) were used to compute V _max (three-parameter models), critical velocity (CV), anaerobic running capacity (ARC) and V _{800 m} from times to exhaustion during CVT. V _max estimates were significantly lower than (0.19<Bias<0.24 m s⁻¹) and poorly associated (0.44<r<0.49) with actual V _max (8.43±0.33 m s⁻¹). Critical velocity (CV) alone explained 40–62% of the variance in V _{800 m}. Combining CV with other parameters of each model to produce a calculated V _{800 m} resulted in a clear improvement of this relationship (0.83<r<0.94). Three-parameter models had a better association (0.93<r<0.94) and a lower bias (0.00<Bias<0.04 m s⁻¹) with actual V _{800 m} (5.87±0.49 m s⁻¹) than two-parameter models (0.83<r<0.91, 0.06<Bias<0.20). If three-parameter models appear to have a better predictive value for short duration events such as the 800 m, the fact the V _max is not associated with the ability it is supposed to reflect suggests that they are more empirical than systems models.     

Are voluntary wheel running and open-field behavior correlated in mice? Different answers from comparative and artificial selection approaches

Voluntary wheel running and open-field behavior are probably the two most widely used measures of locomotion in laboratory rodents. We tested whether these two behaviors are correlated in mice using two approaches: the phylogenetic comparative method using inbred strains of mice and an ongoing artificial selection experiment on voluntary wheel running. After taking into account the measurement error and phylogenetic relationships among inbred strains, we obtained a significant positive correlation between distance run on wheels and distance moved in the open-field for both sexes. Thigmotaxis was negatively correlated with distance run on wheels in females but not in males. By contrast, mice from four replicate lines bred for high wheel running did not differ in either distance covered or thigmotaxis in the open field as compared with mice from four non-selected control lines. Overall, results obtained in the selection experiment were generally opposite to those observed among inbred strains. Possible reasons for this discrepancy are discussed.     

Effects of altitude on the energetics of human best performances in 100 m running: a theoretical analysis

The present study was designed to investigate the role of reduced air density on the energetics of 100 m running at altitude. A mathematical supply-demand model was used where supply had two components, aerobic and anaerobic and demand had three components: the cost of overcoming non-aerodynamic forces (C_na), the cost of overcoming air resistance (C_aero), and the cost due to changes in the runner's kinetic energy (C_kin). Actual instantaneous-speed curves recorded in 100 m world champions were modelled at sea level. Then I calculated improvements in 100 m running times and changes in the components of the energy cost with changes in altitude from 0 m to 4,000 m. For the 100 m world championship for men, the model predicted times of 9.88 s at sea level, 9.80 s at 1,000 m, 9.73 s at 2,000 m, 9.64 s at 4,000 m and 9.15 s in the hypothetical situation where the air resistance was nil. In the counterpart for women the corresponding times were 10.85 s, 10.76 s, 10.70 s, 10.60 s and 10.04 s. The C_aero was 12%–13% of demand at sea level, 10%–11% at 2,000 m and 8%–9% at 4,000 m. When C_aero decreased this led to better performance by making more energy available for acceleration. Accordingly, C_kin increased from 20%–24% at sea level to 23%–27% at 4,000 m. There was no effect of altitude specific to body size. Electronic Publication     

Age-related degeneration in leg-extensor muscle–tendon units decreases recovery performance after a forward fall: compensation with running experience

The goals of this study were to investigate whether the lower muscle-tendon units (MTUs) capacities in older affect their ability to recover balance with a single-step after a fall, and to examine whether running experience enhances and protects this motor skill in young and old adults. The investigation was conducted on 30 older and 19 younger divided into two subgroups: runners versus non-active. In previous studies we documented that the older had lower leg extensor muscle strength and tendon stiffness while running had no effect on MTUs capacities. The current study examined recovery mechanics of the same individuals after an induced forward fall. Younger were better able to recover balance with a single-step compared to older (P < 0.001); this ability was associated with a more effective body configuration at touchdown (more posterior COM position relative to the recovery foot, P <0.001). MTUs capacities classified 88.6% of the subjects into single- or multiple-steppers. Runners showed a superior ability to recover balance with a single-step (P < 0.001) compared to non-active subjects due to a more effective mechanical response during the stance phase (greater knee joint flexion, P <0.05). We concluded that the age-related degeneration of the MTUs significantly diminished the older adults' ability to restore balance with a single-step. Running seems to enhance and protect this motor skill. We suggested that runners, due to their running experience, could update the internal representation of mechanisms responsible for the control of dynamic stability during a forward fall and, thus, were able to restore balance more often with a single-step compared to the non-active subjects.     

In a hot–dry environment racewalking increases the risk of hyperthermia in comparison to when running at a similar velocity

The purpose of this study was to determine if in a hot–dry environment, racewalking increases intestinal temperature (T_int) above the levels observed when running either at the same velocity or at a similar rate of heat production. Nine trained racewalkers exercised for 60 min in a hot–dry environment (30.0 ± 1.4°C; 33 ± 8% relative humidity; 2.4 m s⁻¹ air speed) on three separate occasions: (1) racewalking at 10.9 ± 1.0 km h⁻¹ (Walk), (2) running at the same velocity (RunVel) and (3) running at 13 ± 1.8 km h⁻¹ to obtain a similar [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} than during Walk (Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ). As designed, energy expenditure rate was similar during Walk and Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , but lower during RunVel (842 ± 78 and 827 ± 75 vs. 713 ± 55 W; p < 0.01). Final T_int was lower during RunVel than during both Walk and Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (38.4 ± 0.3 vs. 39.2 ± 0.4 and 39.0 ± 0.4°C; p < 0.01). Heart rate and sweat rate were also lower during RunVel than during Walk and Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (i.e. heart rate 159 ± 13 vs. 179 ± 11 and 181 ± 11 beats min⁻¹ and sweat rate 0.8 ± 0.3 vs. 1.1 ± 0.3 and 1.1 ± 0.3 L h⁻¹; p < 0.01). However, we could not detect differences in skin temperature among trials. In conclusion, our data indicate that in a hot–dry environment racewalking increases the risk of hyperthermia in comparison with when running at a similar velocity. However, exercise mode (walking vs. running) had no measurable impact on T_INT or heat dissipation when matched for energy expenditure.     

Does an increase in energy return and/or longitudinal bending stiffness shoe features reduce the energetic cost of running?

European Journal of Applied Physiology - This study focused on the effects of shoe energy return and shoe longitudinal bending stiffness on the energetic cost and biomechanics of running. The...     

The effects of running exercise on oxidative capacity and PGC-1α mRNA levels in the soleus muscle of rats with metabolic syndrome

Skeletal muscles in animals with metabolic syndrome exhibit reduced oxidative capacity. We investigated the effects of running exercise on fiber characteristics, oxidative capacity, and mRNA levels in the soleus muscles of rats with metabolic syndrome [SHR/NDmcr-cp (cp/cp); CP]. We divided 5-week-old CP rats into non-exercise (CP) and exercise (CP-Ex) groups. Wistar-Kyoto rats (WKY) were used as the control group. CP-Ex rats were permitted voluntary exercise on running wheels for 10 weeks. Triglyceride levels were higher and adiponectin levels lower in the CP and CP-Ex groups than in the WKY group. However, triglyceride levels were lower and adiponectin levels higher in the CP-Ex group than in the CP group. The soleus muscles in CP-Ex rats contained only high-oxidative type I fibers, whereas those in WKY and CP rats contained type I, IIA, and IIC fibers. Muscle succinate dehydrogenase (SDH) activity was higher in the CP-Ex group than in the CP group; there was no difference in SDH activity between the WKY and CP-Ex groups. Muscle proliferator-activated receptor γ coactivator-1α (PGC-1α) mRNA levels were higher in the CP-Ex group than in the CP group; there was no difference in PGC-1α mRNA levels between the WKY and CP-Ex groups. In CP-Ex rats, longer running distance was associated with increased muscle SDH activity and PGC-1α mRNA levels. We concluded that running exercise restored decreased muscle oxidative capacity and PGC-1α mRNA levels and improved hypertriglyceridemia in rats with metabolic syndrome.