A Ramp versus Step Transition to Constant Work Rate Exercise Decreases Steady-State Oxygen Uptake.

PURPOSE: This study aimed to investigate whether a ramp-to-constant WR (rCWR) transition compared with a square-wave-to-constant WR (CWR) transition within the heavy-intensity domain can reduce metabolic instability and decrease the oxygen cost of exercise. METHODS: Fourteen individuals performed (i) a ramp-incremental test to task failure, (ii) a 21-min CWR within the heavy-intensity domain, and (iii) an rCWR to the same WR. Oxygen uptake (V̇O 2 ), lactate concentration ([La - ]), and muscle oxygen saturation (SmO 2 ) were measured. V̇O 2 and V̇O 2 gain (V̇O 2 -G) during the first 10-min steady-state V̇O 2 were analyzed. [La - ] before, at, and after steady-state V̇O 2 and SmO 2 during the entire 21-min steady-state exercise were also examined. RESULTS: V̇O 2 and V̇O 2 -G during rCWR (2.49 ± 0.58 L·min -1 and 10.7 ± 0.2 mL·min -1 ·W -1 , respectively) were lower ( P < 0.001) than CWR (2.57 ± 0.60 L·min -1 and 11.3 ± 0.2 mL·min -1 ·W -1 , respectively). [La - ] before and at steady-state V̇O 2 during the rCWR condition (1.94 ± 0.60 and 3.52 ± 1.19 mM, respectively) was lower than the CWR condition (3.05 ± 0.82 and 4.15 ± 1.25 mM, respectively) ( P < 0.001). [La - ] dynamics after steady-state V̇O 2 were unstable for the rCWR ( P = 0.011). SmO 2 was unstable within the CWR condition from minutes 4 to 13 ( P < 0.05). CONCLUSIONS: The metabolic disruption caused by the initial minutes of square-wave exercise transitions is a primary contributor to metabolic instability, leading to an increased V̇O 2 -G compared with the rCWR condition approach. The reduced early reliance on anaerobic energy sources during the rCWR condition may be responsible for the lower V̇O 2 -G.

The influence of midsole horizontal and vertical deformation on soft tissue vibrations and bone acceleration during running.

Increased midsole deformation can limit exposure to high impact and vibration magnitudes while running. The aim of this study was to evaluate the effect of shoes eliciting different midsole deformation on ground reaction forces, heel impact, soft tissue vibrations and bone vibrations. Forty-eight runners performed a 5-min running task on an instrumented treadmill at a self-selected pace with four different shoes. Midsole horizontal and vertical deformations were quantified with relative displacement of seven reflective markers placed on the midsole of the shoe and tracked by eight optoelectronic cameras. Heel impacts, soft tissue and bone vibrations of lower leg muscle groups, sacrum and head were quantified with tri-axial accelerometers. Continuous wavelet transform was used to assess magnitude and frequency of the acceleration data. Linear mixed models and non-parametric one-dimensional regressions between the accelerometer data and shoe deformation were performed. Greater horizontal and vertical deformations decreased the magnitude (up to 4.6% per mm) and frequency (up to 0.6 Hz per mm) of soft tissue vibrations and bone accelerations. Accelerations of the heel, tibia, gastrocnemius medialis and vastus lateralis were more influenced than the sacrum and head. Increasing midsole deformation could therefore mitigate the risk of injury, while increasing running comfort and smoothness.

Reliability of Soft Tissue Vibration Measurement and Number of Steps Demanded during Treadmill Running.

The present study aims to determine the test-retest reliability of the input signal (INPUT) of foot impact and soft tissue vibration (STV) of the lower limb muscles during treadmill running. Twenty-six recreational runners participated in three running trials at constant velocity (10 km/h) within two days. The INPUT and STV of gastrocnemius medialis (GAS) and vastus lateralis (VL) were extracted from 100 steps measured by three triaxial accelerometers. The Intraclass Correlation Coefficient (ICC) was calculated to determine the Intra-trial and Inter-day reliability of the different variables. Intra-trial reliability results indicated that most of the INPUT and GAS STV parameters, except for damping coefficient and setting time, have good to excellent reliability (0.75 < ICC < 0.9) from the beginning of the run (10 steps) to the end. In contrast, only 4 VL STV parameters showed good reliability. Furthermore, inter-trial reliability measured on day one showed that the number of reliable parameters reduced, especially for VL STV, and more steps were required (20 < steps < 80) to achieve good reliability. Inter-day reliability results showed that only one VL STV parameter reached good reliability. Therefore, the present results show that the measurement of the foot impact and the calf muscle vibrations present a good to excellent reliability measured on a single trial and two trials carried out on the same day. The reliability of these parameters remains good when comparing two days of experimentation. We recommend measuring impact and STV parameters during treadmill running in the same session.

Intra-cycle analysis of muscle vibration during cycling.

Cyclists are exposed for a long period to continuous vibrations. When a muscle is exposed to vibration, its efficiency decreases, the onset of fatigue occurs sooner, and the comfort of the cyclist is reduced. This study characterised the vastus lateralis (VL) soft tissue vibrations for different input frequencies and different pedalling phases. Ten cyclists were recruited to pedal at 55, 70, 85, and 100 rpm on a vibrating cycle ergometer that induced vibrations at frequencies ranging from 14.4 Hz (55 rpm) to 26.3 Hz (100 rpm). The VL vibration amplitude was quantified with a continuous wavelet transform and expressed as a function of the crank angle. The pedalling cycle was split into four phases (downstroke, backstroke, upstroke, and overstroke) to express the mean vibration amplitude and frequency of each phase. Statistical analysis depicted that VL vibration frequency increased with the pedalling cadence and that the VL was exposed to up to 50% more vibration amplitudes during the downstroke phase at a slow cadence. The increase in the pedal vibration frequency, a higher vibration transmission due to greater normal force on the pedal, and strong activation of the VL during the downstroke phase were discussed to explain these results.

Does neuromuscular fatigue generated by trail running modify foot-ground impact and soft tissue vibrations?

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 gastrocnemius medialis (GAS) and vastus lateralis (VL) muscles during level treadmill running at 10 km·h-1. A continuous wavelet transform was used to analyze the acceleration signals in the time-frequency domain, and the maps of coefficients as well as the frequency and damping properties of STV were computed. Fatigue was assessed from isometric maximal voluntary contraction force loss of knee extensors (KE) and plantar flexors (PF) after each race. Statistical nonParametric Mapping and linear mixed models were used to compare the means between the data obtained before and after the races. FGI amplitude and GAS STV were not modified after the race, while VL STV amplitude, frequency and damping significantly decreased whatever the running distance. A significant force loss was observed for the PF (26 ± 14%) and KE (27 ± 16%), but this was not correlated to the changes observed in STV. These results might reveal a protection mechanism of the muscles, indicating that biomechanical and/or physiological adaptations may occur in mountain ultramarathons to limit STV and muscle damage of knee extensors.Trial registration: ClinicalTrials.gov identifier: NCT04025138..

Trail running races with distances from 40 to 171 km induced the same alterations of soft-tissue vibrations. Due to the hilly characteristics of trail running, only the vastus lateralis soft-tissue vibrations were affected by the races.Vastus lateralis vibration amplitude, frequency and damping coefficient were reduced after trail running races. These modifications can arise from a protection mechanism and/or modification in the muscle properties.Neuromuscular fatigue quantified with loss of maximal isometric force production is not predictive of soft-tissue vibration modifications.

Soft Tissue Vibrations in Running: A Narrative Review.

During running, the human body is subjected to impacts generating repetitive soft tissue vibrations (STV). They have been frequently discussed to be harmful for the musculoskeletal system and may alter running gait. The aims of this narrative review were to: (1) provide a comprehensive overview of the literature on STV during running, especially why and how STV occurs; (2) present the various approaches and output parameters used for quantifying STV with their strengths and limitations; (3) summarise the factors that affect STV. A wide set of parameters are employed in the literature to characterise STV. Amplitude of STV used to quantify the mechanical stress should be completed by time-frequency approaches to better characterise neuromuscular adaptations. Regarding sports gear, compression apparels seem to be effective in reducing STV. In contrast, the effects of footwear are heterogeneous and responses to footwear interventions are highly individual. The creation of functional groups has recently been suggested as a promising way to better adapt the characteristics of the shoes to the runners' anthropometrics. Finally, fatigue was found to increase vibration amplitude but should be investigated for prolonged running exercises and completed by an evaluation of neuromuscular fatigue. Future research needs to examine the individual responses, particularly in fatigued conditions, in order to better characterise neuromuscular adaptations to STV.

Angle specific analysis of hamstrings and quadriceps isokinetic torque identify residual deficits in soccer players following ACL reconstruction: a longitudinal investigation.

 Analysing the isokinetic curve is important following ACL reconstruction as there may be deficits in torque production at specific points throughout the range of motion. We examined isokinetic (60°.s-1) torque-angle characteristics in 27 male soccer players (24.5 ± 3.9 years) at 3 time-points (17 ± 5; 25 ± 6; and 34 ± 7 weeks post-surgery). Extracted data included knee flexor and extensor peak torque, conventional hamstrings: quadriceps (H/Q) ratio, and angle-specific torque using Statistical Parametric Mapping (SPM). There were significant involved limb increases in extension peak torque at each assessment (p<0.001); however, asymmetry favouring the un-involved limb was observed (p<0.01). Flexion peak torque was greater on the un-involved limb at assessments 1 and 2 only (p<0.05). The angle of peak torque was not significantly different at individual time-points or within-limbs across the 3 assessments. SPM revealed involved limb angle-specific reductions in extension torque across the full range of motion at time-points 1 and 2 (p<0.001) but only in angles [51-80°] at assessment 3 (p<0.05). Between limb H/Q angle differences [33-45°] were shown at assessments 2 and 3. The ratio ranged from 1.60-0.74 depending on the angle tested. Angle-specific moment curves are useful for monitoring patterns of strength development during rehabilitation.

Combining proactive transcranial stimulation and cardiac biofeedback to substantially manage harmful stress effects.

BACKGROUND: Previous studies have identified the dorsolateral prefrontal cortex (dlPFC) as a core region in cognitive emotional regulation. Transcranial direct current stimulations of the dlPFC (tDCS) and heart-rate variability biofeedback (BFB) are known to regulate emotional processes. However, the effect of these interventions applied either alone or concomitantly during an anticipatory stress remains unexplored. OBJECTIVE: The study investigated the effect of anodal tDCS and BFB, alone or combined, on psychophysiological stress responses and cognitive functioning. METHODS: Following a stress anticipation induction, 80 participants were randomized into four groups and subjected to a 15-min intervention: neutral video viewing (ctrl), left dlPFC anodal tDCS (tdcs), heart-rate variability biofeedback (bfb), or a combined treatment (bfb + tdcs). Participants were then immediately confronted with the stressor, which was followed by an assessment of executive functions. Psychophysiological stress responses were assessed throughout the experiment (heart rate, heart-rate variability, salivary cortisol). RESULTS: The tdcs did not modulate stress responses. Compared with both ctrl and tdcs interventions, bfb reduced physiological stress and improved executive functions after the stressor. The main finding revealed that bfb + tdcs was the most effective intervention, yielding greater reduction in psychological and physiological stress responses than bfb. CONCLUSIONS: Combining preventive tDCS with BFB is a relevant interventional approach to reduce psychophysiological stress responses, hence offering a new and non-invasive treatment of stress-related disorders. Biofeedback may be particularly useful for preparing for an important stressful event when performance is decisive.

Influence of Fatigue on the Rapid Hamstring/Quadriceps Force Capacity in Soccer Players.

The objective of this study was to examine the effect of fatigue on maximal and rapid force capacities and muscular activation of the knee extensors and flexors. Seventeen professional soccer players volunteered to participate in this study. Peak torque (Tpeak) and rate of torque development (RTD) of knee flexor (90°. s-1, -30°. s-1) and extensor (90°. s-1) muscles were measured before and after fatigue (i.e., 30 maximal knee extension and flexion repetitions at 180°s-1) performed on an isokinetic dynamometer. Hamstring to quadriceps peak strength and RTD ratios were calculated. Besides, using surface EMG, the mean level of activation (RMSmean), Rate of EMG Rise (RER), and EMG Frequency-Time maps were measured on quadriceps and hamstring muscles. Following fatigue, Tpeak, RTD, RER declined significantly in the two muscle groups (all p < 0.05) without modification of RMSmean. No decrease in conventional and functional H/Q ratios was observed after fatigue except for a significant increase in the H ecc30/Q con180 ratios (1.03 ± 0.19 vs. 1.36 ± 0.33, p < 0.001). Besides, the RTD H/Q ratios decreased significantly after fatigue, and the statistical parametric mapping analysis (SPM) performed on the EMG/angle curves, and EMG Frequency-Time maps showed that fatigue strongly influenced the muscle activation during the first 100 ms of the movement, following the higher EMG frequency component shift toward the lower frequency component. Our results show that the reduction of RTD and RER during the first 100 ms of the contraction after fatigue exercise makes more sense than any H/Q ratio modification in understanding injury risk in soccer players.

Running patterns and force-velocity sprinting profiles in elite training young soccer players: A cross-sectional study.

The Volodalen® field method permits to classify runners into aerial or terrestrial, based on vertical oscillation, upper-body motion, pelvis and foot position at ground contact, and foot strike pattern. The present study aimed to compare the sprint running force-velocity profiles between aerial and terrestrial runners. Sixty-Four French National-Level young soccer players (28 females, 36 males) performed three trials of unloaded maximal 40 m sprints. External horizontal power-force-velocity relationships were computed using a validated biomechanical model and based on the velocity-time curve. Accordingly, the participants were classified into patterns in aerial and terrestrial runners. Terrestrial runners showed a higher maximal horizontal force (F0) (6.73 ± 1.03 vs 6.01 ± 0.94 N·kg-1), maximal horizontal power (Pmax) (14.04 ± 3.24 vs 12.51 ± 3.31W·kg-1), maximal acceleration (Acc) (6.83 ± 0.85 vs 6.26 ± 0.89 m·s-2), and maximal rate of horizontal force (RFmax) (57.41 ± 4.64 vs 52.81 ± 5.69%) compared to aerial runners. In contrast, terrestrial runners displayed a more negative rate of decrease of RF (DRF) (-11.65 ± 1.71 vs -10.23 ± 1.66%) and slope of the Force-Velocity relationship (F-V slope) (-0.83 ± 0.11 vs -0.77 ± 0.10 N·s·m-1·kg-1) than aerial runners. The results indicate that terrestrial runners displayed more efficient force production in the forward direction and displayed more "force-oriented" F-V profiles. Nevertheless, aerial runners were more effective in maintaining a net horizontal force production with increasing speed. Our results suggest that terrestrial runners could be more adapted to the specific short distance and high acceleration sprints running.

Is Accelerometry an Effective Method to Assess Muscle Vibrations in Comparison to Ultrafast Ultrasonography?

OBJECTIVE: The purpose of this study was to assess whether accelerometry effectively reflects muscle vibrations measured with ultrafast ultrasonography. METHODS: Vibration characteristics initiated on the vastus lateralis muscle by an impactor were compared when assessed with accelerometry and ultrasonography. Continuous wavelet transforms and statistical parametric mapping (SPM) were performed to identify discrepancies in vibration power over time and frequency between the two devices. RESULTS: The SPM analysis revealed that the accelerometer underestimated the muscle vibration power above 50 Hz during the first 0.06 seconds post impact. Furthermore, the accelerometer overestimated the muscle vibration power under 20 Hz, from 0.1 seconds after the impact. Linear regression revealed that the thicker the subcutaneous fat localized under the accelerometer, the more the muscle vibration frequency and damping were underestimated by the accelerometer. CONCLUSION: The skin and the fat tissues acted like a low-pass filter above 50 Hz and oscillated in a less damped manner than the muscle tissue under 20 Hz. SIGNIFICANCE: To eliminate some artifacts caused by the superficial tissues and assess the muscle vibration characteristics with accelerometry, it is suggested to 1) high-pass filter the acceleration signal at a frequency of 20 Hz, under certain conditions, and 2) include participants with less fat thickness. Therefore, the subcutaneous thickness must be systematically quantified under each accelerometer location to clarify the differences between subjects and muscles.

The Immediate Effects of Self-Myofacial Release on Flexibility, Jump Performance and Dynamic Balance Ability.

Self-myofascial release (SMR) is a popular method to potentially increase the compliance and extensibility of the fascia and reduce muscle stiffness. The purpose of this study was to examine the acute effects of posterior muscle chain SMR on flexibility, vertical jump performance and balance ability. Eighteen young participants volunteered to take part in this crossover design study. They performed two self-massage sessions in randomized order separated by at least one week. One session consisted of posterior muscle chain SMR whereas the other one was performed on the upper limbs as a control intervention (CON). Flexibility was measured with the Toe Touch Test (TTT), Weight-Bearing Lunge Test (WBLT), and Straight Leg Raise Test (SLR). Jump performance was evaluated during a squat jump, a counter movement jump and a stiffness jump. Dynamic balance ability was assessed through the Star Excursion Balance Test. All these variables were measured before and after each intervention. A significant increase in flexibility (+3.5 ± 1.8 cm, +1.6 ± 1.0°, and +7.7 ± 4.0° for the TTT, WLBT, and SLR, respectively, p < 0.003) and balance performance (4.8 ± 3.9 cm, p < 0.003) was observed following SMR intervention compared to CON. Conversely, jumping performance was unchanged in both groups. SMR improves joint flexibility and dynamic balance ability.

Input and Soft-Tissue Vibration Characteristics during Sport-Specific Tasks.

PURPOSE: To assess the influence of sport-specific tasks on the characteristics of input and soft-tissue vibrations. METHODS: Triaxial accelerometers were used to quantify the input (heel cup of the shoe) and soft-tissue vibrations of the gastrocnemius medialis and vastus lateralis muscles during seven sport-specific tasks performed by 10 healthy volunteers. A wavelet analysis was used to analyze the acceleration signals in the time-frequency domain. The energy and frequency of the input and soft-tissue vibrations, as well as the transmission of energy from the input to the muscles and the damping properties of soft tissues, were computed. RESULTS: Different inputs, energy transmissions, and damping properties were found between the various movements. Landings and side cuts induced the greatest input frequency and energy, as well as the greatest soft-tissue vibration energy. These tasks produced up to three times greater energy than in-line running. Positive energy transmission was found for frequencies under 50 Hz and for frequencies up to 90 Hz for some movements, indicating a possible change in the natural frequency of vibration within muscle. Only small differences in damping properties were found, which may indicate that the attenuation of the vibration was not the priority during these tasks. CONCLUSIONS: Athletes are subject to greater energy impacts and vibrations during some sport-specific tasks compared with running. It may be useful to decrease such input/vibration energy via the usage of footwear or compression tools to limit their potential deleterious effects on the musculoskeletal system. It is, therefore, recommended to quantify and control the number of impacts induced by the different sport-specific tasks.

Monitoring heart rates to evaluate pacing on a 75-km MUM.

BACKGROUND: To examine pacing among twelve males on a 75-km mountain ultra marathon (MUM) and to determine whether pacing relates to final performance. METHODS: Speed and heart rates (HR) were measured continuously using a HR monitor and a global position system device. An Index of Pacing (IP) was calculated by dividing the average race speed by the speed on the first race segment. In addition, percentage (%) of heart rate reserve (HRres), coefficient of variation (CV) in speed and in percentage of HRres were analyzed throughout the race. RESULTS: Performance time was correlated with IP (r=-0.88, P<0.01), % of HRres (r=- 0.72, P<0.05), and CV in % of HRres (r=0.80, P<0.05), but not with CV in speed (r=-0.12, P=0.9). On the entire race, evolution of HR was not dependent on the elevation gain. CONCLUSIONS: Tracking HR is a safer way to rate pacing than speed tracking on a hilly course.

Performance Factors in a Mountain Ultramarathon.

This study aimed to determine mountain ultra-marathon (MUM) performance factors in a large group of endurance mountain runners. Maximal aerobic speed (MAS) was assessed one week prior to the MUM. The level and graded (10%) energy cost of running, stiffness, knee extensors force (KEf), and jump height on a counter movement jump (CMJ) were measured in 24 male ultra runners before (pre) and immediately after (post) the Interlacs Trail (75 km and 3 930/3 700 m d+/d-). Performance time was correlated with MAS (r=- 0.74, p<0.001), fraction of MAS (FMAS) sustained (r=- 0.89, p<0.001), KEf (r=- 0.51, p<0.05), and KEf loss (r=- 0.51, p<0.05). A multiple regression analysis was performed using performance time in minutes (T) and the calculated individual characteristics, resulting in T=- 11.852×FMAS-37.195×MAS-0.118×KEf+2090.581 (R2=0.98, with 95% confidence interval). Contrary to expectations, performance was neither correlated to the level or uphill energy cost of running nor to the changes of these costs post-MUM. To perform in a MUM, training should take into account muscle strength of the KE, MAS and FMAS.