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The purpose of the study was to assess the influence of a preceding mountain ultramarathon on the impact between the foot and the ground and the resulting soft tissue vibrations (STV). Two sessions of measurements were performed on 52 trail runners, before and just after mountain trail running races of various distances (from 40 to 171 km). Triaxial accelerometers were used to quantify the foot-ground impact (FGI) and STV of both

Hintzy, F, Gregoire, N, Samozino, P, Chiementin, X, Bertucci, W, and Rossi, J. Effect of thigh-compression shorts on muscle activity and soft-tissue vibration during cycling. J Strength Cond Res 33(8): 2145-2152, 2019-This study examined the effects of different levels of thigh compression (0, 2, 6, and 15 mm Hg) in shorts on both vibration and muscle activity of the thigh during cycling with superimposed vibrations. Twelve healthy males performed a 18-minute rectangular cycling test per shorts condition (randomized cross-over design) on a specifically designed vibrating cycloergometer. Each test was composed of 2 intensity levels (moderate then high) and 3 vibration frequencies of 18.3, 22.4, and 26.3 Hz, corresponding to cadences of 70, 85, and 100 rpm, respectively. Muscle vibrations were measured with 2 triaxial accelerometers located before and on the lower-body compression garment, to quantify, respectively, the input and output vibrations, and vastus lateralis muscle activity was measured using surface electromyography. Both vibration and electromyography signals were measured throughout the tests and quantified using root-mean-square analyses. The study showed that the use of a thigh-compression shorts at 6-15 mm Hg significantly reduced both the vibration transmissibility to the thigh and the muscle activity, with higher effect size at higher superimposed vibrations. The thigh-compression shorts garment therefore seems to be 1 way to dampen vibrations transmitted to the cyclists and then to reduce the negative consequences of these vibrations on muscles.

The aim of this study was to investigate the effect of using poles on foot-ground interaction during trail running with slopes of varying incline. Ten runners ran on a loop track representative of a trail running field situation with uphill (+9°), level and downhill (-6°) sections at fixed speed (3.2 m.s(-1)). Experimental conditions included running with (WP) and without (NP) the use of poles for each of the three slopes. Several quantitative and temporal foot-ground interaction parameters were calculated from plantar pressure data measured with a portable device. Using poles induced a decrease in plantar pressure intensity even when the running velocity stayed constant. However, the localisation and the magnitude of this decrease depended on the slope situations. During WP level running, regional analysis of the foot highlighted a decrease of the force time integral (FTI) for absolute (FTIabs; -12.6%; P

A theoretical integrative approach is proposed to understand the overall mechanical characteristics of lower extremities determining jumping ability. This approach considers that external force production during push-off is limited by mechanical constraints imposed by both movement dynamics and force generator properties, i.e. lower extremities characteristics. While the velocity of the body depends on the amount of external force produced over the push-off, the capabilities of force production decrease with increasing movement velocity, notably for force generators driven by muscular contraction, such as lower extremities of large animals during jumping from a resting position. Considering the circular interaction between these two mechanical constraints, and using simple mathematical and physical principles, the proposed approach leads to a mathematical expression of the maximal jump height an individual can reach as a function of only three integrative mechanical characteristics of his lower extremities: the maximal force they can produce ( F ¯ 0 ), the maximal velocity at which they can extend under muscles action ( v ¯ 0 ) and the distance of force production determined by their usual extension range ( h PO ). These three integrative variables positively influence maximal jump height. For instance in humans, a 10% variation in F ¯ 0 , v ¯ 0 or h PO induces a change in jump height of about 10–15%, 6–11% and 4–8%, respectively. The proposed theoretical approach allowed to isolate the basic mechanical entities through which all physiological and morphological specificities influence jumping performance, and may be used to separate the very first macroscopic effects of these three mechanical characteristics on jumping performance variability.

Non-circular chainrings alter the crank velocity profile over a pedalling cycle. The aim of this study was to investigate the effect of this altered crank velocity profile on the aerobic performance compared to a circular chainring (CC). Ten male non-cyclists performed two incremental maximal tests at 80 rpm on a cycle ergometer: one with a circular (Shimano) and the other with a non-circular chainring Osymetric® (Somovedi), at least 50 h apart. Each test started with a workload of 100 W lasting 3 min. During the first 12 min, the workload was increased by 30 W every 3 min. Thereafter, the workload was increased by 30 W every 2 min until exhaustion. The power output, the intra-cycle crank angular velocity and the physiological parameters were monitored continuously, averaged over the last 30 s of each increment and at exhaustion, and compared for the two chainrings. Results showed a higher maximal aerobic power attained with the non-circular chainring (362.6 ± 37.9 vs. 338.8 ± 32.6 W, p

The purpose of this study was to investigate the interactions between cadence and power output effects on cycling efficiency. Fourteen healthy subjects performed four constant power output-tests (40, 80, 120 and 160 W) in which the cadence varied in five bouts from 40 to 120 rpm. Gross efficiency (GE) was determined over the last ten respiratory cycles of each bout and was calculated as the ratio of mechanical energy to energy expenditure. Results showed that (1) GE-cadence relationships reached a maximum at each power output corresponding to the cadence maximising efficiency (CAeff) and (2) GE increased with power output whatever the cadence until a maximal theoretical value. Moreover, interactions were found between these two factors: the cadence effect decreased linearly with power output and the power output effect increased exponentially with cadence. Consequently, cycling efficiency decreased more when cadence differed from CAeff at low than at high power output, and increased more with power output at high cadence than at low cadence. These interactions between cadence and power output effects on GE were mainly due to cadence and power output effects on the energy expenditure shares not contributing to power production.

To determine the optimal pedalling rate that minimises both the oxygen consumption (fV(O2,min)) and the energy cost of cycling (f(Cr,min)), 22 male subjects were asked to cycle on an ergometer on five occasions of 4 min each at a constant power output of 150 W and at pedalling rates of 40, 60, 80, 100 and 120 rpm. The oxygen consumption (V(O2) in millilitres per minute per kilogram) and the energy cost (Cr in joules per kilogram per metre) were determined during each period. The individual V(O2)-pedalling rate and Cr-pedalling rate relationships were fitted by parabolic regressions which allowed the determination for each individual of fV(O2,min) [mean (SD) 57.0 (4.9) rpm] and f(Cr,min) [101.1 (3.2) rpm], respectively. Contrary to the values obtained for fV(O2,min), those for f(Cr,min) were in agreement with the pedalling rates (90-110 rpm) usually selected in road cycling. It is therefore suggested that the minimisation of Cr is the main factor that determines the pedalling rate in field conditions. The lack of a significant correlation between fV(O2,min) and f(Cr,min) further indicated that, although fV(O2,min) is often used for determining the metabolic capacities of subjects, f(Cr,min) is a better index of optimal mechanical parameters of cycling in field conditions.

The aim of this study was to compare optimal pedalling velocities during maximal (OVM) and submaximal (OVSM) cycling in human, subjects with different training backgrounds. A group of 22 subjects [6 explosive (EX), 6 endurance (EN) and 10 non-specialised subjects] sprint cycled on a friction-loaded ergometer four maximal sprints lasting 6 s each followed by five 3-min periods of steady-state cycling at 150 W with pedalling frequencies varying from 40 to 120 rpm. The OVM and OVSM were defined as the velocities corresponding to the maximal power production and the lowest oxygen consumption, respectively. A significant linear relationship (r2 = 0.52, P < 0.001) was found between individual OVM [mean 123.1 (SD 11.2) rpm] and OVSM [mean 57.0 (SD 4.9) rpm, P < 0.001] values, suggesting that the same functional properties of leg extensor muscles influence both OVM and OVSM. Since EX was greater than EN in both OVM and OVSM (134.3 compared to 110.9 rpm and 60.8 compared to 54.0 rpm, P < 0.01 and P < 0.05, respectively) it could be hypothesised that the distribution of muscle fibre type plays an important role in optimising both maximal and submaximal cycling performance.

The purpose of the present experiment was to investigate the immediate effects of a cycling exercise on postural control during quiet standing in healthy young adults. To this aim, 12 university students were asked to stand upright as immobile as possible, with their eyes closed, prior to and following a 15 min cycling exercise performed at a power output of 200 W. Centre of foot pressure (CP) displacements, recorded using a force platform along both the medio-lateral (ML) or antero-posterior (AP) axes, were used to compute the motions of the vertical projection of the centre of gravity (CG(v)) and those of the difference between the CP and the CG(v) (CP - CG(v)). Metabolic (heart rate, respiratory exchange ratio and blood lactate concentration) and psychological (rate of perceived exertion) measurements ensured that subjects were fatigued at the end of the cycling exercise. The cycling exercise induced a decreased of both CG(v) and CP - CG(v) motions along the AP-axis, whereas no significant changes were observed along the ML-axis. These discrepancies of the postural effects according to the direction of balance are likely to stem from the directionally sensitive activity of postural muscles, when considering (1) what the cycling exercise involved in terms of joints and tendons receptors stimulation and lower limb muscles recruitment (i.e. sagittal plane movers of the lower extremities) and (2) the skeletal muscles involved in postural control during quiet standing (i.e. sagittal and frontal plane movers of the lower extremities for the AP and ML balance, respectively).

This study proposed a non-invasive method to determine the gross (GE, no baseline correction), net (NE, resting metabolism as the baseline correction) and work (WE, unloaded cycling as the baseline correction) efficiencies during cycling at an intensity higher than the maximal aerobic power (MAP). Twelve male subjects performed two exercises consisting of 4 min at 50% MAP followed either by 8 min at 63% MAP or by 8 sequences of 60 s divided into 10 s at 130% MAP and 50 s at 50% MAP (i.e., 63% MAP on average). Oxygen uptake was continuously measured to calculate GE, NE and WE at 50%, 63% and 130% MAP, and the data presented as the means and standard deviations. The GE values were 18.2%, 19.1%, 22.7%, the NE values were 22.4%, 22.8%, 24.3% and the WE values were 34.2%, 31.4% and 27.2% at 50%, 63% and 130% MAP, respectively. The GE and NE increased (P

The effects of endurance training in normoxia or in hypoxia on time to exhaustion ( T(lim)) at the work rate corresponding to peak oxygen uptake (VO(2peak)) were examined at sea level in 13 healthy subjects. Before and after training the subjects performed the following: (1) incremental exercises up to exhaustion to determine peak oxygen uptake in normoxia (VO(2peak)N), the percentage of this value at the 4 mmol l(-1) blood lactate concentration (VO(2)4%N) and the work rate corresponding to VO(2peak)N (Pa(peak)N), (2) a 5-min 90% Pa(peak)N exercise followed by a 10-min passive recovery to determine the maximal blood lactate concentration (La(max)) measured during the recovery, and (3) a T(lim) at Pa(peak)N. Training consisted of pedalling 2 h a day, 6 days a week, for 4 weeks. Five subjects trained in normobaric hypoxia [HT; partial pressure of inhaled oxygen ( P(I)O(2)) 89 mmHg] and eight subjects trained at the same relative work rates in normoxia (NT; P(I)O(2) 141 mmHg). The training-induced improvement of all the measured parameters were closely matched between the HT and the NT ( P0.05). Training increased T(lim) by 59.7% [164(40) s]. The value of T(lim) was related to VO(2)4%N and to La(max) before and after training. Also, the training-induced improvement of T(lim) was related to the concomitant decrease in La(max). It is concluded that: (1) endurance training including continuous high-intensity exercises improves T(lim) for exercises performed at the same relative (higher absolute) work rate after training, (2) intermittent hypoxic training has no potentiating effect on T(lim) as compared with training in normoxia, and (3) the intra-individual training-induced improvement of T(lim) was associated with metabolic alteration in relation to lactate accumulation.

The present study aimed to investigate the effects of a high-intensity swim test among top-level swimmers on (i) the spatial and temporal parameters of both the stroke and the 3-D fingertip pattern and (ii) the mechanical, muscular, and physiological parameters. Ten male international swimmers performed a 4 × 50 m swim at maximal intensity. Isometric arm flexion force with the elbow at 90° (F90°), EMG signals of right musculus biceps brachii and triceps brachii and blood lactate concentrations were recorded before and after the swim test. Kinematic stroke (stroke length, rate, and velocity) and spatiotemporal parameters of the fingertip trajectory were measured by two underwater cameras during the first and last 50 m swims. After the swim test, F90° and mean power frequencies of the EMG decreased significantly when blood lactate concentration increased significantly, attesting the reaching of fatigue. From the first to the last 50 m, stroke rate, stroke velocity, and temporal parameters of the fingertip trajectory exhibited significant increases although stroke length and spatial fingertip trajectory remained unchanged. General and individual adaptations were observed among the top-level swimmers studied. The present findings could be useful for coaches in evaluating fatigue effects on the technical parameters of swimming.Key words: sport, fatigue, biomechanic, lactate, force.