Synergistic difference in the effect of stretching on electromechanical delay components.

This study investigated the synergistic difference in the effect of stretching on electromechanical delay (EMD) and its components, using a simultaneous recording of electromyographic, mechanomyographic, and force signals. Twenty-six healthy men underwent plantar flexors passive stretching. Before and after stretching, the electrochemical and mechanical components of the EMD and the relaxation EMD (R-EMD) were calculated in gastrocnemius medialis (GM), lateralis (GL) and soleus (SOL) during a supramaximal motor point stimulation. Additionally, joint passive stiffness was assessed. At baseline, the mechanical components of EMD and R-EMD were longer in GM and GL than SOL (Cohen's d from 1.78 to 3.67). Stretching decreased joint passive stiffness [-22(8)%, d = -1.96] while overall lengthened the electrochemical and mechanical EMD. The mechanical R-EMD components were affected more in GM [21(2)%] and GL [22(2)%] than SOL [12(1)%], with d ranging from 0.63 to 1.81. Negative correlations between joint passive stiffness with EMD and R-EMD mechanical components were found before and after stretching in all muscles (r from -0.477 to -0.926; P from 0.007 to <0.001). These results suggest that stretching plantar flexors affected GM and GL more than SOL. Future research should calculate EMD and R-EMD to further investigate the mechanical adaptations induced by passive stretching in synergistic muscles.

Energetics of sinusoidal exercise below and across critical power and the effects of fatigue.

PURPOSE: Previous studies investigating sinusoidal exercise were not devoted to an analysis of its energetics and of the effects of fatigue. We aimed to determine the contribution of aerobic and anaerobic lactic metabolism to the energy balance and investigate the fatigue effects on the cardiorespiratory and metabolic responses to sinusoidal protocols, across and below critical power (CP). METHODS: Eight males (26.6 ± 6.2 years; 75.6 ± 8.7 kg; maximum oxygen uptake 52.8 ± 7.9 ml·min-1·kg-1; CP 218 ± 13 W) underwent exhausting sinusoidal cycloergometric exercises, with sinusoid midpoint (MP) at CP (CPex) and 50 W below CP (CP-50ex). Sinusoid amplitude (AMP) and period were 50 W and 4 min, respectively. MP, AMP, and time-delay (tD) between mechanical and metabolic signals of expiratory ventilation ( V ˙ E ), oxygen uptake ( V ˙ O 2 ), and heart rate ( f H ) were assessed sinusoid-by-sinusoid. Blood lactate ([La-]) and rate of perceived exertion (RPE) were determined at each sinusoid. RESULTS: V ˙ O 2 AMP was 304 ± 11 and 488 ± 36 ml·min-1 in CPex and CP-50ex, respectively. Asymmetries between rising and declining sinusoid phases occurred in CPex (36.1 ± 7.7 vs. 41.4 ± 9.7 s for V ˙ O 2 tD up and tD down, respectively; P < 0.01), with unchanged tDs. V ˙ O 2 MP and RPE increased progressively during CPex. [La-] increased by 2.1 mM in CPex but remained stable during CP-50ex. Anaerobic contribution was larger in CPex than CP-50ex. CONCLUSION: The lower aerobic component during CPex than CP-50ex associated with lactate accumulation explained lower V ˙ O 2 AMP in CPex. The asymmetries in CPex suggest progressive decline of muscle phosphocreatine concentration, leading to fatigue, as witnessed by RPE.

Speed Effects on the Accuracy of Heart Rate as Oxygen-Uptake Indicator in Short-Distance Shuttle Running.

Purpose: Despite the accuracy of heart rate (HR) as an indicator of the aerobic engagement has been evaluated in several intermittent on-court activities, its validity as an oxygen uptake (V˙O2) indicator during shuttle running over short paths remains uncertain. Moreover, it is unclear whether speed may affect such validity. This study evaluated the HR ability in estimating the V˙O2 during 5-m shuttle running at different speeds. Methods: V˙O2 and HR of 12 physically active young men were recorded during an incremental forward running (FW) protocol and a 5-m shuttle test at 50%, 60%, and 75% of maximal aerobic speed (MAS). Slope and intercept of the relationship between HR and V˙O2 (HR/V˙O2) were individually determined, in both protocols. The HR measured during the shuttle test was used in the FW HR/V˙O2 to estimate V˙O2 at each shuttle speed. A paired Student's t-test compared slopes and intercepts of the two HR/V˙O2. A two-way RM-ANOVA and an equality test examined, respectively, the differences and the equality between measured and estimated V˙O2. Lastly, a Bland-Altman plot described the accuracy and precision of the estimated V˙O2 at each shuttle intensity. Results: Slopes and intercepts of the HR/V˙O2 appeared not different between FW and shuttle running. At 50%MAS, HR underestimated the V˙O2 (~7%), whereas returned accurate values at the two higher velocities, although with high variability (±18%). Conclusions: When using HR as V˙O2 indicator during shuttle running over short paths, a separated analysis of the HR validity as V˙O2 indicator is recommended especially when administering different exercise intensities.

Is the Interpolated-Twitch Technique-Derived Voluntary Activation Just Neural? Novel Perspectives from Mechanomyographic Data.

PURPOSE: Voluntary activation (VA) determined by interpolation-twitch technique could be affected by the characteristics of the in-series elastic components. To overcome this possible bias, a novel approach based on the mechanomyographic (MMG) signal to detect voluntary activation (VA MMG ) has been proposed. We examined the changes in VA and VA MMG after passive stretching to check the influence of neural and mechanical factors in the force output. METHODS: Twenty-six healthy men underwent VA assessment using the interpolated-twitch technique before and after unilateral passive stretching of the plantarflexors (five 45-s on + 15-s off). In addition to the force signal, the MMG signal was detected on gastrocnemius medialis, gastrocnemius lateralis, and soleus. From the force and MMG signal analysis, VA and VA MMG were calculated in the stretched and contralateral nonstretched limbs. Joint passive stiffness was also defined. RESULTS: In the stretched limb, passive stretching increased dorsiflexion range (mean ± SD = +18% ± 10%, P < 0.001, ES = 1.54) but reduced joint passive stiffness (-22% ± 8%, P < 0.001, ES = -1.75), maximum voluntary contraction (-15% ± 7%, P < 0.001, ES = -0.87), VA (-7% ± 3%, P < 0.001, ES = -2.32), and VA MMG (~-5% ± 2%, P < 0.001, ES = -1.26/-1.14). In the contralateral nonstretched limb, passive stretching increased dorsiflexion range (+10% ± 6%, P < 0.001, ES = 0.80) but reduced joint passive stiffness (-3% ± 2%, P = 0.041, ES = -0.27), maximum voluntary contraction (-4% ± 3%, P = 0.035, ES = -0.24), VA (-4% ± 2%, P < 0.001, ES = -1.77), and VA MMG (~- 2% ± 1%, P < 0.05, ES = -0.54/-0.46). The stretch-induced changes in VA correlated with VA MMG ( R ranging from 0.447 to 0.583 considering all muscles) and with joint passive stiffness (stretched limb: R = 0.503; contralateral nonstretched limb: R = 0.530). CONCLUSIONS: VA output is overall influenced by both neural and mechanical factors, not distinguishable using the interpolated-twitch technique. VA MMG is a complementary index to assess the changes in VA not influenced by mechanical factors and to examine synergistic muscles.

Determining voluntary activation in synergistic muscles: a novel mechanomyographic approach.

PURPOSE: Drawing on correlations between the mechanomyographic (MMG) and the force signal, we devised a novel approach based on MMG signal analysis to detect voluntary activation (VA) of the synergistic superficial heads of the quadriceps muscle. We hypothesized that, after a fatiguing exercise, the changes in the evoked MMG signal of each quadriceps head would correlate with the changes in the level of VA in the whole quadriceps. METHODS: Twenty-five men underwent a unilateral single-leg quadriceps exercise to failure. Before and after exercise, VA was assessed by interpolated-twitch-technique via nerve stimulation during and after maximum voluntary contraction (MVC). The force and MMG signal were recorded from vastus lateralis, vastus medialis, and rectus femoris. The MMG peak-to-peak was calculated and the voluntary activation index (VAMMG), defined as the superimposed/potentiated MMG peak-to-peak ratio, was determined from the MMG signal for each head. RESULTS: VAMMG presented a very high intraclass correlation coefficient (0.981-0.998) and sensitivity (MDC95%: 0.42-6.97%). MVC and VA were decreased after exercise in both the exercising [MVC:-17(5)%, ES -0.92; VA: -7(3)%, ES -1.90] and the contralateral limb [MVC: -9(4)%, ES -0.48; VA: -4(1)%, ES -1.51]. VAMMG was decreased in both the exercising [~ -9(6)%, ES -1.77] and contralateral limb [~ -3(2)%, ES -0.57], with a greater decrease in VAMMG noted only in the vastus medialis of the exercising limb. Moderate-to-very high correlations were found between VAMMG and VA (R-range: 0.503-0.886) before and after exercise. CONCLUSION: VAMMG may be implemented to assess VA and provide further information when multiple synergistic muscle heads are involved in fatiguing exercises.

Testing protocol affects the velocity at VO2max in semi-professional soccer players.

To compare three different protocols to assess the velocity associated with the maximal oxygen uptake (Vmax) in soccer players. Sixteen semi-professional soccer players performed three maximum incremental tests on treadmill: two continuous protocols [1 km·h-1·min-1 (CP1); and 1 km·h-1 every 2 min (CP2)], and one discontinuous (DP) protocol to determine Vmax, maximum oxygen uptake (VO2max) and oxygen cost of running (i.e., the slope of the VO2 vs velocity relationship at submaximal exercise). Vmax was higher in CP1> CP2> DP (19.4 ± 1.7, 17.4 ± 1.2, 16.1 ± 1.1 km·h-1 for CP1, CP2, and DP, respectively; P < 0.05 ES: 0.09 to 3.36). No difference in VO2max was found between CP1, CP2 and DP (P > 0.05). Oxygen cost of running showed between-protocol differences (CP1> CP2> DP; P < 0.05; ES: 0.28 to 3.30). Vmax was higher when determined using continuous vs discontinuous protocols due to the greater overestimation in oxygen cost of running. Such differences in Vmax should be considered to optimize acute physiological responses during high-intensity running activities.

Passive stretching decreases muscle efficiency in balance tasks.

The current study aimed to verify whether or not passive static stretching affects balance control capacity. Thirty-eight participants (19 women and 19 men) underwent a passive static stretching session, involving the knee extensor/flexor and dorsi/plantarflexor muscles, and a control session (no stretching, CTRL). Before (PRE), immediately after (POST), after 15 (POST15) and 30 min (POST30) from stretching (or rest in CTRL), balance control was evaluated under static and dynamic conditions, with open/closed eyes, and with/without somatosensory perturbation (foam under the feet). During tests, centre of pressure (CoP) sway area and perimeter and antero-posterior and medio-lateral sway mean speed were computed. Surface electromyography root mean square (sEMG RMS) was calculated from the vastus lateralis, biceps femoris, gastrocnemius medialis, and tibialis anterior muscles during MVC and during the balance tests. Hip flexion/extension and dorsi/plantarflexion range of motion (ROM), maximum voluntary contraction (MVC) and sEMG RMS during MVC were measured at the same time points. After stretching, ROM increased (≈6.5%; P<0.05), while MVC and sEMG RMS decreased (≈9% and ≈7.5%, respectively; P<0.05). Regardless of the testing condition, CoP sway area and the perimeter remained similar, while antero-posterior and medio-lateral sway mean speed decreased by ≈8% and ≈12%, respectively (P<0.05). sEMG RMS during the balance tests increased in all muscles in POST (≈7%, P<0.05). All variables recovered in POST30. No changes occurred in CTRL. Passive static stretching did not affect the overall balance control ability. However, greater muscle activation was required to maintain similar CoP sway, thus suggesting a decrease in muscle efficiency.

Training status affects between-protocols differences in the assessment of maximal aerobic velocity.

PURPOSE: Continuous incremental protocols (CP) may misestimate the maximum aerobic velocity (Vmax) due to increases in running speed faster than cardiorespiratory/metabolic adjustments. A higher aerobic capacity may mitigate this issue due to faster pulmonary oxygen uptake ([Formula: see text]O2) kinetics. Therefore, this study aimed to compare three different protocols to assess Vmax in athletes with higher or lower training status. METHODS: Sixteen well-trained runners were classified according to higher (HI) or lower (LO) [Formula: see text]O2max [Formula: see text]O2-kinetics was calculated across four 5-min running bouts at 10 km·h-1. Two CPs [1 km·h-1 per min (CP1) and 1 km·h-1 every 2-min (CP2)] were performed to determine Vmax [Formula: see text]O2max, lactate-threshold and submaximal [Formula: see text]O2/velocity relationship. Results were compared to the discontinuous incremental protocol (DP). RESULTS: Vmax, [Formula: see text]O2max, [Formula: see text]CO2 and VE were higher [(P < 0.05,(ES:0.22/2.59)] in HI than in LO. [Formula: see text]O2-kinetics was faster [P < 0.05,(ES:-2.74/ - 1.76)] in HI than in LO. [Formula: see text]O2/velocity slope was lower in HI than in LO [(P < 0.05,(ES:-1.63/ - 0.18)]. Vmax and [Formula: see text]O2/velocity slope were CP1 > CP2 = DP for HI and CP1 > CP2 > DP for LO. A lower [P < 0.05,(ES:0.53/0.75)] Vmax-difference for both CP1 and CP2 vs DP was found in HI than in LO. Vmax-differences in CP1 vs DP showed a large inverse correlation with Vmax, [Formula: see text]O2max and lactate-threshold and a very large correlation with [Formula: see text]O2-kinetics. CONCLUSIONS: Higher aerobic training status witnessed by faster [Formula: see text]O2 kinetics led to lower between-protocol Vmax differences, particularly between CP2 vs DP. Faster kinetics may minimize the mismatch issues between metabolic and mechanical power that may occur in CP. This should be considered for exercise prescription at different percentages of Vmax.

The effects of 12 weeks of static stretch training on the functional, mechanical, and architectural characteristics of the triceps surae muscle-tendon complex.

PURPOSE: We investigated the effects of 12 weeks of passive static stretching training (PST) on force-generating capacity, passive stiffness, muscle architecture of plantarflexor muscles. METHODS: Thirty healthy adults participated in the study. Fifteen participants (STR, 6 women, 9 men) underwent 12-week plantarflexor muscles PST [(5 × 45 s-on/15 s-off) × 2exercises] × 5times/week (duration: 2250 s/week), while 15 participants (CTRL, 6 women, 9 men) served as control (no PST). Range of motion (ROM), maximum passive resistive torque (PRTmax), triceps surae architecture [fascicle length, fascicle angle, and thickness], passive stiffness [muscle-tendon complex (MTC) and muscle stiffness], and plantarflexors maximun force-generating capacity variables (maximum voluntary contraction, maximum muscle activation, rate of torque development, electromechanical delay) were calculated Pre, at the 6th (Wk6), and the 12th week (Wk12) of the protocol in both groups. RESULTS: Compared to Pre, STR ROM increased (P < 0.05) at Wk6 (8%) and Wk12 (23%). PRTmax increased at Wk12 (30%, P < 0.05), while MTC stiffness decreased (16%, P < 0.05). Muscle stiffness decreased (P < 0.05) at Wk6 (11%) and Wk12 (16%). No changes in triceps surae architecture and plantarflexors maximum force-generating capacity variables were found in STR (P > 0.05). Percentage changes in ROM correlated with percentage changes in PRTmax (ρ = 0.62, P = 0.01) and MTC stiffness (ρ = - 0.78, P = 0.001). In CTRL, no changes (P > 0.05) occurred in any variables at any time point. CONCLUSION: The expected long-term PST-induced changes in ROM were associated with modifications in the whole passive mechanical properties of the ankle joint, while maximum force-generating capacity characteristics were preserved. 12 weeks of PST do not seem a sufficient stimulus to induce triceps surae architectural changes.

Acute carnosine and ß-alanine supplementation increase the compensated part of the ventilation versus work rate relationship during a ramp incremental cycle test in physically active men.

BACKGROUND: Chronic supplementation with carnosine and ß-alanine (Carn-ßA) has been proposed to improve muscle contractility and reduce muscle fatigue mainly through an increase in intracellular pH buffering capacity. However, the acute ergogenic effects of Carn-ßA supplementation are poorly investigated. This study aimed at evaluating the acute effects of a single Carn-ßA supplementation on the cardiorespiratory and metabolic response during a ramp cycle-ergometric test. METHODS: This randomized, double-blind, placebo-controlled study, involved 10 healthy males (age: 22.2±1.9 years, body mass: 72.5±7.9 kg, stature: 1.72±0.08 m, Body Mass Index: 24.47±1.91 kg/m2, mean±standard deviation). All the participants performed two maximal incremental ramp tests on a cycle ergometer, with a prior randomized assumption of 2.5 g L-carnosine plus 2.5 g ß-alanine (Carn-ßA) or placebo (PLA). During exercise, gas exchange parameters were measured breath-by-breath, heart rate was monitored by electrocardiography and rate perceived exertion was determined on Borg scales. From the ramp test, peak cardiorespiratory and metabolic parameters and ventilatory thresholds (VT1 and VT2) were calculated offline. RESULTS: No differences between the experimental conditions emerged at peak exercise. However, despite acute Carn-ßA supplementation did not affect the single ventilatory thresholds, the compensated portion of the ramp test (i.e. the difference between VT2 and VT1) was significantly larger (P=0.043) in Carn-ßA. CONCLUSIONS: These findings demonstrate a positive effect of acute Carn-ßA supplementation on the compensated part of the exercise. This should be taken into account by nutritionists and athletes searching for nutritional supplements, when a quick effect based on an acute dose is required.

Local fat content and muscle quality measured by a new electrical impedance myography device: correlations with ultrasound variables.

AbstractThe present study investigated the relationship between local fat percentage (SKfat) and muscle quality (MQ) estimated by a new hand-held electrical impedance myography (hEIM) device or derived from ultrasound and strength assessments. The right anterior thigh of 90 healthy participants (mean ± SD; age=22.9 ± 2.9 years; 45 men: BMI = 23.9 ± 2.4 kgm-2; 45 women: BMI = 21.1 ± 1.9 kgm-2) was scanned by hEIM and ultrasound. Correlations between SKfat, local subcutaneous fat (SUBfat), and echo intensity (EIus) were explored. Correlations between MQ, EIus, quadriceps femoris anatomical cross-sectional area (ACSAQF), knee extensors maximum voluntary isometric torque (T), T/ACSAQF, EIus/SUBfat, and ACSAQF/SUBfat were also assessed. SKfat correlated with SUBfat (r = 0.88; p < 0.001) and EIus (r = 0.64; p < 0.001). MQ correlated with EIus (r = -0.66; p < 0.001), ACSAQF (r = 0.37; p < 0.001), EIus/SUBfat (r = 0.37; p < 0.001), and ACSAQF/SUBfat (r = 0.81; p < 0.001). Multiple regression analysis showed that SUBfat, EIus, and sex explained 86% of SKfat variance, whereas ACSAQF/SUBfat, sex and EIus explained 75% of MQ variance. In conclusion, high hEIM local fat percentage relates to greater subcutaneous fat and intramuscular non-contractile tissue content. High hEIM muscle quality relates to greater muscle-size:subcutaneous-fat ratio and contractile tissue content. Sex influences the prediction of both parameters. This hEIM device seems to be useful to estimate local thigh composition.

On-Sight and Red-Point Climbing: Changes in Performance and Route-Finding Ability in Male Advanced Climbers.

AIM: In lead climbing, the ascent of the route can be defined as on-sight or red-point. On-sight is the more challenging style since it demands greater physiological and psychological commitment. The differences between the two modes in advanced climbers have not been studied much. Two essential skills needed to optimize performance, in both on-sight and in red-point climbing, are route interpretation (RI) ability and movements sequence recall. Therefore, this study aimed to compare performance between on-sight and red-point ascent in advanced climbers and evaluate how a climber's RI ability and movement sequences recall might change before and after on-sight and red-point climbing. METHODS: Eighteen advanced male climbers (age 29.2 ± 4.7 years, body mass 67.8 ± 3.6 kg, stature 175.2 ± 2.4 cm, best red-point and on-sight grades 7b+/8a and 7a+/7b+, respectively) were video-recorded during the route ascent in on-sight and red-point modes to evaluate performance and to measure static and dynamic action times. RI ability and movement sequence recall were assessed before and after each climb. Level of anxiety was evaluated via a self-report questionnaire. Heart rate (f H), lactate concentration, ([La-]), and rating of perceived exertion (RPE) were detected during and after each climb. RESULTS: Compared to on-sight, an improvement in performance was observed in a red-point climb: the ascent was faster (148.7 ± 13.6 s and 179.5 ± 12.5 s, respectively, P < 0.05), smoother (significant reduction in exploratory moves and in stops times, P < 0.05), less demanding physiologically (lower f H peak and [La-]peak, P < 0.05), and psychologically (lower RPE, cognitive and somatic anxiety and higher self-confidence, P < 0.05). The RI ability was improved in red-point versus on-sight and, in the same mode, between pre and post ascent. CONCLUSION: Red-point climbing was found to be less demanding than on-sight, both physiologically and psychologically, under the conditions investigated by this study. Our findings suggest that RI is a trainable skill and underscore the importance of including specific techniques in training programs designed to improve interaction between perceptual, psychological, and physiological factors.

Neuromuscular versus Mechanical Stretch-induced Changes in Contralateral versus Ipsilateral Muscle.

PURPOSE: Whether or not the homologous contralateral muscle (CM) undergoes stretch-induced force reduction as the stretched muscle (SM) is still unclear. The neuromuscular and mechanical factors underlying the force reduction in CM and SM were investigated. METHODS: Twenty-one participants underwent unilateral knee extensors passive stretching. In both CM and SM, before, immediately after (POST), 5 (POST5), and 10 min (POST10) after passive stretching, maximum voluntary contraction (MVC), peak force (pF), and voluntary activation (VA) were measured. During MVC, the electromyographic and mechanomyographic root mean square (EMG RMS and MMG RMS, respectively) was calculated in rectus femoris, vastus lateralis, and vastus medialis, together with M-wave. The total electromechanical delay (EMD), divided in time delay (Δt) EMG-MMG and Δt MMG-F was calculated. RESULTS: In CM at POST, the decrease in MVC (-11%; 95% confidence interval [CI], -13 to -9; effect size [ES], -2.27) was accompanied by a fall in VA (-7%; 95% CI, -9 to -4; ES, -2.29), EMG RMS (range, -22% to -11%; ES, -3.92 to -2.25), MMG RMS (range, -10% to -8%; ES, -0.52 to -0.39) and an increase in Δt EMG-MMG (≈+10%; ES, 0.73 to 0.93). All changes returned to baseline at POST5. In SM, decrease in MVC (-19%; 95% CI, -24 to -18; ES, -3.08), pF (-25%; 95% CI, -28 to -22; ES, -4.90), VA (-10%; 95% CI, -11 to -9; ES, -5.71), EMG RMS (≈-33%; ES, -5.23 to -3.22) and rise in MMG RMS (range, +25% to +32%; ES, 4.21 to 4.98) and EMD (≈+28%; ES, 1.59 to 1.77) were observed at POST and persisted at POST10. No change in M-wave occurred. CONCLUSIONS: The contralateral central motor drive stretch-induced inhibition seems to account for the force reduction in CM. In SM, both central inhibition and mechanical factors concurred.

Quadriceps and Gastrocnemii Anatomical Cross-Sectional Area and Vastus Lateralis Fascicle Length Predict Peak-Power and Time-To-Peak-Power.

Purpose: The current study investigated the role of quadriceps and gastrocnemii size and vastus lateralis and gastrocnemius medialis muscle architecture in peak-power and time-to-peak-power exerted in an all-out Wingate test. Twenty-one amateur cyclists were recruited. Methods: Quadriceps and gastrocnemii anatomical cross-sectional area (ACSA), and vastus lateralis and gastrocnemius medialis pennation angle and fascicle length were measured using ultrasound. Relative peak-power (normalized per body mass) and time-to-peak-power were measured during a 30s all-out test. Results: Relative peak-power was correlated with quadriceps ACSA (r = 0.896, p < .001), gastrocnemii ACSA (r = 0.811, p < .001), vastus lateralis (r = 0.787, p < .001) and gastrocnemius medialis pennation angle (r = 0.638, p < .003). Multiple regression revealed that quadriceps and gastrocnemii ACSA accounted for 85% (R2= 0.85) of peak-power variance. Time-to-peak-power showed very large (r = -0.868, p < .001) and large correlation (r = -0.680, p = .001) with VL and GM fascicle length, respectively. Multiple regression analysis revealed that VL fascicle length explained 75% (R2= 0.75) of the time-to-peak-power variance. Conclusions: Quadriceps and gastrocnemii ACSA largely explained relative peak-power in an all-out Wingate test. Vastus lateralis fascicle length was the main predictor of the time-to-peak-power. Muscle architecture characteristics seem to be involved in the power generating capacity.

Peripheral fatigue: new mechanistic insights from recent technologies.

Peripheral fatigue results from multiple electrochemical and mechanical events in the cell body and the muscle-tendon complex. Combined force and surface electromyographic signal analysis is among the most widely used approaches to describe the behaviour of a fatigued muscle. Advances in technologies and methodological procedures (e.g. laser diffraction, 31P magnetic resonance spectroscopy, shear-wave elastography, tensiomyography, myotonometry, mechanomyography, and high-density surface electromyography) have expanded our knowledge of muscle behaviour before, during, and after a fatiguing task. This review gives an update on recent developments in technologies for investigating the effects of peripheral fatigue linked to skeletal muscle contraction and on mechanistic insights into the electrochemical and mechanical aspects of fatigue. The salient points from the literature analysis are: (1) the electrochemical and mechanical events in the cell (alterations in cross-bridge formation and function and in depolarization of the tubular membrane) precede the events taking place at the muscle-tendon complex (decrease in muscle-tendon unit stiffness); (2) the changes in the fatigued muscle are not homogenous along its length and width but rather reflect a functional compartmentalisation that counteracts the decline in performance; (3) fatigue induces changes in load sharing among adjacent/synergistic muscles. A focus of future studies is to observe how these regional differences occur within single muscle fibres. To do this, a combination of different approaches may yield new insights into the mechanisms underlying muscle fatigue and how the muscle counteracts fatigue.

Evidence of Improved Vascular Function in the Arteries of Trained but Not Untrained Limbs After Isolated Knee-Extension Training.

Vascular endothelial function is a strong marker of cardiovascular health and it refers to the ability of the body to maintain the homeostasis of vascular tone. The endothelial cells react to mechanical and chemical stimuli modulating the smooth muscle cells relaxation. The extent of the induced vasodilation depends on the magnitude of the stimulus. During exercise, the peripheral circulation is mostly controlled by the endothelial cells response that increases the peripheral blood flow in body districts involved but also not involved with exercise. However, whether vascular adaptations occur also in the brachial artery as a result of isolated leg extension muscles (KE) training is still an open question. Repetitive changes in blood flow occurring during exercise may act as vascular training for vessels supplying the active muscle bed as well as for the vessels of body districts not directly involved with exercise. This study sought to evaluate whether small muscle mass (KE) training would induce improvements in endothelial function not only in the vasculature of the lower limb (measured at the femoral artery level in the limb directly involved with training), but also in the upper limb (measured at the brachial artery level in the limb not directly involved with training) as an effect of repetitive increments in the peripheral blood flow during training sessions. Ten young healthy participants (five females, and five males; age: 23 ± 3 years; stature: 1.70 ± 0.11 m; body mass: 66 ± 11 kg; BMI: 23 ± 1 kg ⋅ m-2) underwent an 8-week KE training study. Maximum work rate (MWR), vascular function and peripheral blood flow were assessed pre- and post-KE training by KE ergometer, flow mediated dilatation (FMD) in the brachial artery (non-trained limb), and by passive limb movement (PLM) in femoral artery (trained limb), respectively. After 8 weeks of KE training, MWR and PLM increased by 44% (p = 0.015) and 153% (p = 0.003), respectively. Despite acute increase in brachial artery blood flow during exercise occurred (+25%; p < 0.001), endothelial function did not change after training. Eight weeks of KE training improved endothelial cells response only in the lower limb (measured at the femoral artery level) directly involved with training, likely without affecting the endothelial response of the upper limb (measured at the brachial artery level) not involved with training.

Heart and musculoskeletal hemodynamic responses to repetitive bouts of quadriceps static stretching.

The role of sympathetic and parasympathetic activity in relation to the repetitive exposure to static stretching (SS) on heart and musculoskeletal hemodynamics in stretched and resting muscles is still a matter of debate. The aim of the study was to determine cardiac and musculoskeletal hemodynamics to repetitive bouts of unilateral SS. Sympathetic and parasympathetic activity contribution to the central hemodynamics and local difference in circulation of stretched and resting muscles were also investigated. In eight participants, heart rate (HR), cardiac output (CO), mean arterial pressure (MAP), HR variability (HRV), blood pressure variability (BPV), and blood flow in passively stretched limb (SL) and control (CL, resting limb) were measured during five bouts of unilateral SS (45 s of knee flexion and 15 s of knee extension). SS increased sympathetic (~20%) and decreased parasympathetic activity (~30%) with a prevalence of parasympathetic withdrawal. During SS, HR, CO, and MAP increased by ~18 beats/min, ~0.29 l/min, ~12 mmHg, respectively. Peak blood flow in response to the first stretching maneuver increased significantly (+377 ± 95 ml/min) in the SL and reduced significantly (-57 ± 48 ml/min) in the CL. This between-limb difference in local circulation response to SS disappeared after the second SS bout. These results indicate that heart hemodynamic responses to SS are primarily influenced by the parasympathetic withdrawal rather than by the increase in sympathetic activity. The balance between neural and local factors contributing to blood flow regulation was affected by the level of SS exposure, likely associated with differences in the bioavailability of local vasoactive factors throughout the stretching bouts.NEW & NOTEWORTHY Repetitive exposure to static stretching (SS) on heart and musculoskeletal hemodynamics in stretched and remote muscles may be influenced by neural and local factors. We documented that SS-induced heart hemodynamic responses are primarily influenced by parasympathetic withdrawal. The balance between neural and local factors contributing to the regulation of musculoskeletal hemodynamics is dependent on SS exposure possibly because of different local vasoactive factor bioavailability during the subsequent stretching bouts.

Effect of ramp slope on different methods to determine lactate threshold in semi-professional soccer players.

The present study aimed to investigate the effect of stage duration in incremental protocols on lactate threshold (LT), determined by different methods. Sixteen semi-professional soccer-players performed a 4-min stage incremental discontinuous (DP) and two maximal incremental running continuous (1 km h-1· min-1, CP1; and 1 km h-1·2 min-1 CP2) protocols. Blood-lactate concentration [La-] was measured at baseline and during the protocols. LT was determined using DMAX, DMAX-MOD, 4-mM⋅L-1, Δ1-mM⋅L-1 and Log-Log methods. Log-Log showed no difference in LT between CP1, CP2 and DP. Conversely, LT was determined at higher velocity in CP1 than CP2 for DMAX (15.2 ± 0.5 vs 14.4 ± 1.2 km⋅h-1, P = 0.002), DMAX-MOD (16.0 ± 0.5 vs 14.7 ± 1.3 km⋅h-1, P < 0.001), 4-mM⋅L-1 (15.5 ± 1.4 vs 14.4 ± 1.2 km⋅h-1, P < 0.001), Δ1-mM⋅L-1 (15.5 ± 1.3 vs 14.4 ± 1.2 km⋅h-1, P < 0.001). Higher LT in CP1 than DP for DMAX (15.2 ± 0.5 vs 13.0 ± 1.0 km⋅h-1, P < 0.001) and DMAX-MOD (16.0 ± 0.5 vs 13.6 ± 1.6 km⋅h-1, P < 0.001) was found (P < 0.001). Log-Log resulted in shorter but accurate protocols to determine LT.

Heart rate and pulmonary oxygen uptake response in professional badminton players: comparison between on-court game simulation and laboratory exercise testing.

PURPOSE: Badminton is characterized by bouts of high intensity interspersed by short recovery periods. Aerobic assessment via indirect calorimetry is impractical on court because of the encumbrance of portable metabolic devices. When the relationship between heart rate (HR) and pulmonary oxygen uptake [Formula: see text] [Formula: see text] is linear, HR monitoring can provide an indirect estimation of metabolic demands on court. However, owing to the intermittent nature of badminton, the [Formula: see text] relationship will differ from that obtained in the laboratory, making its use on court questionable. The aims of this study were to (i) assess cardiorespiratory and metabolic responses during on-court badminton rally simulations at different intensities and (ii) compare [Formula: see text] relationships obtained from laboratory and on-court measurements. METHODS: The study sample was seven professional badminton players (age 16.9 ± 2.1 years; body mass 62.8 ± 9.2 kg; stature 1.71 ± 0.09 m). [Formula: see text] HR, and other respiratory and metabolic parameters were assessed in the laboratory with an incremental intermittent Astrand-type test (IIAT) and on court during rally simulations at three different intensities. RESULTS: Cardiorespiratory parameters measured during the rallies reached 95% of maximal IIAT values. The [Formula: see text] slope and intercept differed in the on-court and the IIAT conditions (P = 0.012 and P = 0.008, respectively). CONCLUSIONS: The difference in [Formula: see text] regression lines between the IIAT and the on-court condition indicates that HR monitoring may not provide accurate data on the aerobic demands of specific on-court badminton tasks. HR monitoring should be preceded by an indirect calorimetry test on court to assess aerobic demands more precisely.

Energy Cost of Continuous Shuttle Running: Comparison of 4 Measurement Methods.

Ciprandi, D, Lovecchio, N, Piacenza, M, Limonta, E, Esposito, F, Sforza, C, Zago, M. Energy cost of continuous shuttle running: Comparison of 4 measurement methods. J Strength Cond Res 32(8): 2265-2272, 2018-Assessing runs with frequent turns (shuttle run) is a viable option to evaluate the energy cost associated with sport-specific high-intensity intermittent activities. To date, no study investigated the extent to which the computation of energy cost of exercise is affected by the following factors: procedure and duration of oxygen uptake measurement during exercise, oxygen uptake measurement during recovery, estimation of the anaerobic alactic contribution, consideration of respiratory exchange ratio (RER) in the computation, and exercise intensity. Therefore, the aim of the current study was to determine whether these factors may lead to different estimations of the energy cost of locomotion. Twenty-six healthy young men participated in two 5-m shuttle-run trials at an average speed of 50 and 75% of their maximal aerobic velocity, respectively. Oxygen uptake and lactate concentration were measured before, during, and after the trials. Results revealed that different methods of computing the energy cost of 5-m shuttle run returned significantly different results, in particular at high intensity levels. The largest significant difference found between methods was lower than 10%. This suggests that for the most accurate computation of the workload, the contribution of the anaerobic alactic mechanisms and the influence of the RER cannot be neglected. These findings might help sport scientists and conditioning trainers in identifying the exercise conditions in which including all the metabolic components are required for an accurate computation of athletes' energy expenditure. In turn, exercise conditions would be defined where the computation could be conveniently simplified without worsening results reliability.