This experiment investigated the fatigue induced by a 24-h running exercise (24TR) and particularly aimed at testing the hypothesis that the central component would be the main mechanism responsible for neuromuscular fatigue. Neuromuscular function evaluation was performed before, every 4 h during, and at the end of the 24TR on 12 experienced ultramarathon runners. It consisted of a determination of the maximal voluntary contractions (MVC) of the knee extensors (KE) and plantar flexors (PF), the maximal voluntary activation (%VA) of the KE and PF, and the maximal compound muscle action potential amplitude (Mmax) on the soleus and vastus lateralis. Tetanic stimulations also were delivered to evaluate the presence of low-frequency fatigue and the KE maximal muscle force production ability. Strength loss occurred throughout the exercise, with large changes observed after 24TR in MVC for both the KE and PF muscles (-40.9+/-17.0 and -30.3+/-12.5%, respectively; P<0.001) together with marked reductions of %VA (-33.0+/-21.8 and -14.8+/-18.9%, respectively; P<0.001). A reduction of Mmax amplitude was observed only on soleus, and no low-frequency fatigue was observed for any muscle group. Finally, KE maximal force production ability was reduced to a moderate extent at the end of the 24TR (-10.2%; P<0.001), but these alterations were highly variable (+/-15.7%). These results suggest that central factors are mainly responsible for the large maximal muscle torque reduction after ultraendurance running, especially on the KE muscles. Neural drive reduction may have contributed to the relative preservation of peripheral function and also affected the evolution of the running speed during the 24TR.

This study aimed to 1) compare electrical and magnetic stimulations for quadriceps muscle function assessment, and 2) ascertain whether the ratios of the second twitch elicited by supramaximal electrical and magnetic femoral nerve stimulation at 10 and 100 Hz (T2(10:100)) and the total twitch force elicited by the same types of stimulations (Fpaired(10:100)) are equivalent to the standard low- to high-frequency force ratio associated with submaximal electrical tetanic stimulations (Ftet(10:100)). Quadriceps force and vastus lateralis EMG were recorded at rest (n = 21 subjects), immediately after, and 30 min after a 30-min downhill run (n = 10) when 1) supramaximal electrical nerve stimulation (ENS), 2) magnetic nerve stimulation (MNS) and 3) submaximal electrical muscle stimulation (EMS) were delivered in random order at 1 (single stimulation), 10, and 100 Hz (paired stimulations). Ten- and 100-Hz 500-ms tetani were also evoked with EMS to determine Ftet(10:100). Before exercise, contractile properties with single and paired stimulations were similar for ENS and MNS (all intraclass correlation coefficients k > 0.90), but smaller for EMS (P < 0.001). M-wave characteristics were also similar for ENS and MNS (all k > 0.90). After exercise, changes in all parameters did not differ between methods. With fatigue, the changes in Ftet(10:100) were inconsistently correlated with the changes in T2(10:100) (r(2) = 0.24-0.73, P = 0.002-0.15) but better correlated with the changes in Fpaired(10:100) (immediately after exercise: r(2) = 0.80-0.83, P < 0.001; 30 min after exercise: r(2) = 0.46-0.82, P = 0.001-0.03). We conclude that ENS and MNS provide similar quadriceps muscle function assessment, while Fpaired(10:100) is a better index than T2(10:100) of low- to high-frequency fatigue of the quadriceps in vivo.

The purpose of this study was to examine the physiological and biological factors associated with ultra-endurance performance. Fourteen male runners volunteered to run on a treadmill as many kilometers as possible over a 24-h period (24TR). Maximal oxygen uptake (VO(2max)), velocity associated with VO(2max)(VO(2max)) and running economy (RE) at 8 km/h were measured. A muscle biopsy was also performed in the vastus lateralis muscle. The subjects ran 149.2 ± 15.7 km in 18 h 39 ± 41 min of effective attendance on the treadmill, corresponding to 39.4 ± 4.2% of . Standard multiple-regression analysis showed that performance was significantly (R(2) = 0.82; P = 0.005) related to VO(2max) and specific endurance, i.e. the average speed sustained over the 24TR expressed in . VO(2max) was associated with a high capillary tortuosity (R(2) = 0.66; P = 0.01). Specific endurance was significantly related to RE and citrate synthase activity. It is concluded that a high VO(2max) and an associated developed capillary network are essential for ultra-endurance running performance. The ability to maintain a high %VO(2max) over a 24TR is another factor associated with performance and is mainly related to RE and high mitochondrial oxidative capacity in the vastus lateralis.

The present study characterized accurately the changes of energy cost and substrate use during an extreme run, showing a plateau after 8 h of exercise. It is also concluded that the participants who maintained the highest %VV˙O2max were also those having most deteriorated their Cr over the 24TR, supporting the notion of a trade-off between running speed (relative to VV˙O2max) and Cr.

Introduction: The aim of this study was to determine whether calf compression sleeves (CS) affects physiological and biomechanical parameters, exercise performance, and perceived sensations of muscle fatigue, pain and soreness during prolonged (~2 h 30 min) outdoor trail running.Methods: Fourteen healthy trained males took part in a randomized, cross-over study consisting in two identical 24-km trail running sessions (each including one bout of running at constant rate on moderately flat terrain, and one period of all-out running on hilly terrain) wearing either degressive CS (23 ± 2 mmHg) or control sleeves (CON, <4 mmHg). Running time, heart rate and muscle oxygenation of the medial gastrocnemius muscle (measured using portable near-infrared spectroscopy) were monitored continuously. Muscle functional capabilities (power, stiffness) were determined using 20 s of maximal hopping before and after both sessions. Running biomechanics (kinematics, vertical and leg stiffness) were determined at 12 km·h−1 at the beginning, during, and at the end of both sessions. Exercise-induced Achilles tendon pain and delayed onset calf muscles soreness (DOMS) were assessed using visual analog scales.Results: Muscle oxygenation increased significantly in CS compared to CON at baseline and immediately after exercise (p < 0.05), without any difference in deoxygenation kinetics during the run, and without any significant change in run times. Wearing CS was associated with (i) higher aerial time and leg stiffness in running at constant rate, (ii) with lower ground contact time, higher leg stiffness, and higher vertical stiffness in all-out running, and (iii) with lower ground contact time in hopping. Significant DOMS were induced in both CS and CON (>6 on a 10-cm scale) with no difference between conditions. However, Achilles tendon pain was significantly lower after the trial in CS than CON (p < 0.05).Discussion: Calf compression did not modify muscle oxygenation during ~2 h 30 of trail running but significantly changed running biomechanics and lower limb muscle functional capabilities toward a more dynamic behavior compared to control session. However, wearing compression sleeves did not affect performance and exercise-induced DOMS, while it minimized Achilles tendon pain immediately after running.

BackgroundExercise intensity during ultramarathons (UM) is expected to be regulated as a result of the development of psycho-physiological strain and in anticipation of perceived difficulties (duration, topography). The aim of this study was to investigate the dynamics of speed, heart rate and perceived exertion during a long trail UM in a mountainous setting.MethodsFifteen participants were recruited from competitors in a 106 km trail mountain UM with a total elevation gain and loss of 5870 m. Speed and gradient, heart rate (HR) and ratings of perceived exertion (dissociated between the general [RPEGEN] and knee extensor fatigue [RPEKE] and collected using a voice recorder) were measured during the UM. Self-selected speed at three gradients (level, negative, positive), HR, RPEGEN and RPEKE were determined for each 10% section of total event duration (TED).ResultsThe participants completed the event in 18.3 ± 3.0 h, for a total calculated distance of 105.6 ± 1.8 km. Speed at all gradients decreased, and HR at all gradients significantly decreased from 10% to 70%, 80% and 90%, but not 100% of TED. RPEGEN and RPEKE increased throughout the event. Speed increased from 90% to 100% of TED at all gradients. Average speed was significantly correlated with total time stopped (r = -.772; p = .001; 95% confidence interval [CI] = -1.15, -0.39) and the magnitude of speed loss (r = .540; p = .038; 95% CI = -1.04, -0.03), but not with the variability of speed (r = -.475; p = .073; 95% CI = -1.00, 0.05).ConclusionsParticipants in a mountain UM event combined positive pacing strategies (speed decreased until 70–90% of TED), an increased speed in the last 10% of the event, a decrease in HR at 70–90% of TED, and an increase in RPEGEN and RPEKE in the last 30% of the event. A greater speed loss and less total time stopped were the factors associated with increased total performance. These results could be explained by theoretical perspectives of a complex regulatory system modulating motor drive in anticipation of perceived difficulties such as elevation changes.

PurposeHigh intensity interval training (HIIT) has been proposed as a time-efficient format of exercise to reduce the chronic disease burden associated with sedentary behaviour. Changes in oxygen utilisation at the local tissue level during an acute session of HIIT could be the primary stimulus for the health benefits associated with this format of exercise. The recovery periods of HIIT effect the physiological responses that occur during the session. It was hypothesised that in sedentary individuals, local and systemic oxygen utilisation would be higher during HIIT interspersed with active recovery periods, when compared to passive recovery periods.MethodsTwelve sedentary males (mean ± SD; age 23 ± 3 yr) completed three conditions on a cycle ergometer: 1) HIIT with passive recovery periods between four bouts (HIITPASS) 2) HIIT with active recovery periods between four bouts (HIITACT) 3) HIITACT with four HIIT bouts replaced with passive periods (REC). Deoxygenated haemoglobin (HHb) in the vastus lateralis (VL) and gastrocnemius (GN) muscles and the pre-frontal cortex (FH), oxygen consumption (VO2), power output and heart rate (HR) were measured continuously during the three conditions.ResultsThere was a significant increase in HHb at VL during bouts 2 (p = 0.017), 3 (p = 0.035) and 4 (p = 0.035) in HIITACT, compared to HIITPASS. Mean power output was significantly lower in HIITACT, compared to HIITPASS (p < 0.001). There was a significant main effect for site in both HIITPASS (p = 0.029) and HIITACT (p = 0.005). There were no significant differences in VO2 and HR between HIITPASS and HIITACT.ConclusionsThe increase in HHb at VL and the lower mean power output during HIITACT could indicate that a higher level of deoxygenation contributes to decreased mechanical power in sedentary participants. The significant differences in HHb between sites indicates the specificity of oxygen utilisation.

Ultraendurance running reduces respiratory muscle strength for inspiratory muscles shown to result from significant peripheral muscle fatigue with only little contribution of central fatigue. This is in contrast to findings in locomotor muscles. Whether this difference between muscle groups results from inherent neuromuscular differences, their specific pattern of loading or other reasons remain to be clarified.