Complexity analysis of surface electromyography for assessing the myoelectric manifestation of muscle fatigue: A review

The surface electromyography (sEMG) records the electrical activity of muscle fibers during contraction: one of its uses is to assess changes taking place within muscles in the course of a fatiguing contraction to provide insights into our understanding of muscle fatigue in training protocols and rehabilitation medicine. Until recently, these myoelectric manifestations of muscle fatigue (MMF) have been assessed essentially by linear sEMG analyses. However, sEMG shows a complex behavior, due to many concurrent factors. Therefore, in the last years, complexity-based methods have been tentatively applied to the sEMG signal to better individuate the MMF onset during sustained contractions. In this review, after describing concisely the traditional linear methods employed to assess MMF we present the complexity methods used for sEMG analysis based on an extensive literature search. We show that some of these indices, like those derived from recurrence plots, from entropy or fractal analysis, can detect MMF efficiently. However, we also show that more work remains to be done to compare the complexity indices in terms of reliability and sensibility; to optimize the choice of embedding dimension, time delay and threshold distance in reconstructing the phase space; and to elucidate the relationship between complexity estimators and the physiologic phenomena underlying the onset of MMF in exercising muscles

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\u2019s 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 \ub1 4.7 years, body mass 67.8 \ub1 3.6 kg, stature 175.2 \ub1 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 (fH), lactate concentration, ([La\u2013]), 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 \ub1 13.6 s and 179.5 \ub1 12.5 s, respectively, P < 0.05), smoother (significant reduction in exploratory moves and in stops times, P < 0.05), less demanding physiologically (lower fHpeak and [La\u2013]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

Cardiovascular and metabolic responses during indoor climbing and laboratory cycling exercise in advanced and élite climbers

Purpose. To validate heart rate (fH) as an effective indicator of the aerobic demands of climbing, the fH vs. oxygen uptake (VO2) relationship determined during cycling exercise and climbing on a circular climbing treadwall was compared. Possible differences in maximum aerobic characteristics between advanced and \ue9lite climbers were also assessed. Methods. Seven advanced and six \ue9lite climbers performed a discontinuous incremental test on a cycle ergometer and a similar test on a climbing treadwall. Cardiorespiratory and gas exchange parameters were collected at rest and during exercise. Results. The fH vs. VO2 relationship was steeper during cycling than climbing at submaximal exercise for both groups and during climbing in the \ue9lite climbers as compared to the advanced. At peak exercise, VO2 was similar during both cycling and climbing (3332\ub1115 and 3193\ub1129 ml/min, respectively). Despite similar VO2 peak, the \ue9lite climbers had a higher peak workload during climbing (11.8\ub10.8 vs. 9.2\ub10.3 m/min in \ue9lite and advanced climbers, respectively; P=.024) but not during cycling (282\ub113 vs. 268\ub112 W in \ue9lite and advanced climbers, respectively). Conclusions. Our findings indicate that care should be taken when energy expenditure during climbing is estimated from the fH vs VO2 relationship determined in the laboratory. The level of climbing experience significantly affects the energy cost of exercise. Lastly, the similar aerobic demands of cycling and climbing at peak exercise, suggest that maximum VO2 may play an important role in climbing performance. Specific training methodologies should be implemented to improve aerobic power in climbers

Kinematic algorithm to determine the energy cost of running with changes of direction

Changes of direction (CoDs) have a high metabolic and mechanical impact in field and court team sports, but the estimation of the associated workload is still inaccurate. This study aims at validating an algorithm based on kinematic data to estimate the energy cost of running with frequent 180\ub0-CoDs. Twenty-six physically active male subjects (22.4\u202f\ub1\u202f3.2\u202fyears) participated in two sessions: (1) maximum oxygen uptake (V\u307O2,max) and maximal aerobic speed (MAS) test; (2) 5-m continuous shuttle run (two 5-min trials at 50% and 75% MAS, 6-min recovery). In (2), full-body 3D-kinematics and V\u307O2 were simultaneously recorded. Actual cost of shuttle running (Cmeas) was obtained from the aerobic, anaerobic alactic and lactic components. The proposed algorithm detects "braking phases", periods of mostly negative (eccentric) work occurring at concurrent knee flexion and ground contact, and estimates energy cost (Cest) considering negative mechanical work in braking phases, and positive elsewhere. At the speed of, respectively, 1.54\u202f\ub1\u202f0.17 and 1.90\u202f\ub1\u202f0.15\u202fm\u202fs-1 (rate of perceived exertion: 9.1\u202f\ub1\u202f1.8 and 15.8\u202f\ub1\u202f1.9), Cmeas was 8.06\u202f\ub1\u202f0.49 and 9.04\u202f\ub1\u202f0.73\u202fJ\u202fkg-1\u202fm-1. Cest was more accurate than regression models found in literature (p\u202f\u202f0.05; average error: 8.3%, root-mean-square error: 0.86\u202fJ\u202fkg-1\u202fm-1). The proposed algorithm improved existing techniques based on CoM kinematics, integrating data of ground contacts and joint angles that allowed to separate propulsive from braking phases. This work constitutes the basis to extend the model from the laboratory to the field, providing a reliable measure of training and matches workload

Evidence of balance training‐induced improvement in soccer‐specific skills in U11 soccer players

The present study aim was to determine the role of balance training in improving technical soccer skills in young players. Two U11 soccer teams were randomly assigned one to either balance training (BT; n=22) or control group (Ctrl; n=21). At the end of their habitual soccer training (identical in BT and Ctrl), BT underwent additional balance training for 12 weeks (3sessions/week, 20 min per session), while Ctrl had a 20\u2010min scrimmage. Before and after the intervention, BT and Ctrl underwent two soccer\u2010specific tests (Loughborough Soccer Passing, LSPT, and Shooting, LSST, Tests), and bipedal and unipedal balance evaluations. After intervention, both groups decreased the trials time and improved passing accuracy, with larger improvements in BT than Ctrl [LSPT penalty time (CI95%): \u20102.20 s (\u20102.72/\u20101.68); ES (CI95%): \u20102.54 s (\u20103.34/\u20101.74)]. Both groups improved balance ability, with BT showing larger increments in bipedal tests than Ctrl [static balance: \u201029 mm (\u201042/\u201016); ES: \u20101.39 (\u20102.05/\u20100.72); limit of stability: 4% (3/5); ES 3.93 (2.90/4.95); unipedal quasi\u2010dynamic balance: 0.07 a.u. (0.03/0.11); ES: 1.04 (0.40/1.67) and active range of motion: \u20105% (\u20108/\u20102); ES \u20100.89 (\u20101.51/\u20100.26)]. Low\u2010to\u2010moderate correlations between the players\u2019 technical level and unipedal balance ability were retrieved, particularly in the non\u2010dominant limb (R from 0.30 to 0.48). Balance training improved some technical soccer skills more than habitual soccer training alone, suggesting that young soccer players may benefit from additional balance training added to their traditional training

The influence of mouth guard usage on neuromuscular activation and performance

Aim: The aim of this study was to investigate the effects of a commercially-available mouth guard (BRUX Mod. Sport) on neuromuscular activation and force capacity. Mouth guards, indeed, are commonly used in different sports to prevent injuries, but it is not yet clear whether they can influence the force expression and some athletes remain wary of the perceived potential performance detriments using them. Method: Ten participants completed a balanced randomized study with (S-MG) and without (Con) a sport mouth guard. Each participant performed two tests, with elbow flexors and knee extensors muscles: 1-min contraction at 100% of maximum voluntary contraction (MVC) and an 80% MVC contraction until exhaustion. During 80% MVC, the time of force within the target (t-target) and the coefficient of variation (CV) of the force signal were calculated. During 100% MVC, force decay (\uf044F%) and the root mean square (RMS) of the electromyogram (EMG) were calculated. Results: MVC values in S-MG were significantly higher than in Con in the elbow flexors (P<0.05). No differences was found in knee extensors muscles. At 80% MVC, no differences in t-target values were observed between Con and S-MG for both muscles group. Conversely, in knee extensors muscles, CV was significantly lower in S-MG compared to Con. During 1-min at 100% MVC contraction, \uf044F% was significantly lower in S-MG than in Con in the elbow-flexors (P<0.05) . Conclusion: Overall, these findings indicate that despite neuromuscular activation was not affected, S-MG usage increased maximum force production, endurance time and force stability, especially in the upper limb muscles. References - Dunn-Lewis, C, Luk, H-Y, Comstock, BA, Szivak, TK, Hooper, DR, Kupchak, BR, Watts, AM, Putney, BJ, Hydren, JR, Volek, JS, Denegar, CR, and Kraemer, WJ. The effects of a customized over-the-counter mouth guard on neuromuscular force and power production in trained men and women. J Strength Cond Res 26(4): 1085\u20131093, 2012. - Cetin, C, Kececi, AD, Erdogan, A, and Baydar, ML. Influence of custom-made mouth guards on strength, speed and anaerobic performance of taekwondo athletes. Dent Traumatol 25: 272\u2013276, 2009. - Bourdin M, Brunet-Patru I, Hager PE, Allard Y, Hager JP, Lacour JR et al. Influence of maxillary mouthguards on physiological parameters. Med Sci Sports Exerc 38:1500\u20134,2006

Specific adaptations in performance and muscle architecture after weighted jump-squat vs body mass squat jump training in recreational soccer players

The aim of the present study was to compare the effects of weighted jump squat (WJST) vs body mass squat jump training (BMSJT) on quadriceps muscle architecture, lower-limb lean-mass (LM) and muscle strength, performance in change of direction (COD), sprint and jump in recreational soccer-players. Forty-eight healthy soccer-players participated in an off-season randomized controlled-trial. Before and after an eight-week training intervention, vastus lateralis pennation angle, fascicle length, muscle thickness, LM, squat 1-RM, quadriceps and hamstrings isokinetic peak-torque, agility T-test, 10 and 30m sprint and squat-jump (SJ) were measured. Although similar increases in muscle thickness, fascicle length increased more in WJST (ES=1.18, 0.82-1.54) than in BMSJT (ES=0.54, 0.40-0.68) and pennation angle only increased in BMSJT (ES=1.03, 0.78-1.29). Greater increases in LM were observed in WJST (ES=0.44, 0.29-0.59) than in BMSJT (ES=0.21, 0.07-0.37). Agility T-test (ES=2.95, 2.72-3.18), 10m (ES=0.52, 0.22-0.82) and 30m-sprint (ES=0.52, 0.23-0.81) improved only in WJST, while SJ improved in BMSJT (ES=0.89, 0.43-1.35) more than in WJST (ES=0.30, 0.03-0.58). Similar increases in squat 1-RM and peak-torque occurred in both groups. The greater inertia accumulated within the landing-phase in WJST vs BMSJT has increased the eccentric workload, leading to specific eccentric-like adaptations in muscle architecture. The selective improvements in COD in WJST may be related to the increased braking ability generated by the enhanced eccentric workload

Cardiorespiratory responses to cycle exercise during a low-intensity sinusoidal work rate

Purpose: Sinusoidal varying protocols have been recently re-proposed in assessing the cardiorespiratory response (CRR) to exercise to reflect the variability in long-lasting physical activities. Contrary to square-wave tests, the cyclic nature of sinusoidal work rate allows to explore the CRR kinetics several times. Previous studies used to overlap CRR of successive periods; however, so far no study assessed whether CRRs are constant along different cycles. Therefore, this study aimed at investigating the CRR during an exhausting low-intensity sinusoidal work rate. Methods: Seven subjects (age: 27 ± 7 yr, body mass: 72.5 ± 6.7 kg; stature: 1.8 ± 0.1 m) participated to the study. After determining on different days the maximum oxygen uptake (V’O2max) by ramp cycle ergometric test and critical power (CP) via different submaximal exercises, they underwent a sinusoidal work rate until exhaustion. The exercise varied according to a sinewave function with a midpoint (MP) equal to 50 W below CP (CP-50), an amplitude (A) of 50 W and a period of 4 min. Expiratory ventilation (V’E), carbon dioxide output (V’CO2), oxygen uptake (V’O2) and heart rate (HR) were obtained breath-by-breath and fitted off-line by the sinewave functions that minimized the residuals. Thereafter, A, MP and the timedelay (tD, the latency between mechanical and CRR signals) were obtained for each cycle. A one-way ANOVA for repeated measures was applied to test the effect of fatigue. Results: MP of V’E, V’O2 and HR significantly increased as well as A of V’E and V’CO2 (p\0.05 for all parameters). On the contrary, A of HR decreased during the test (p\0.05). No changes were detected on tD in all CRRs parameters. Conclusions: This study demonstrates that despite the low intensity level of the sinusoidal protocol, the dynamics of CRRs are not constant. Therefore, averaging the CRRs of different cycles might introduce a bias in the outcomes concealing a marked change in CRRs. References 1. Fukuoka Y et al. (2002) Dynamics of the heart rate response to sinusoidal work in humans: influence of physical activity and age. Clinical Science 102: 31–38 2. Miyamoto Y et al. (1983) Cardiorespiratory Dynamics during Sinusoidal and Impulse Exercise in Man. The Japanese Journal of Physiology 33: 971-98

Local and systemic vascular hemodynamic response to passive static stretching in young healthy humans

The aim of the present study was to determine the acute effects of passive static stretching (PSS) on femoral blood flow (FBF) in a stretched and non-stretched limb. Our hypothesis was that PSS would increase FBF in the stretched limb mainly through local vasodilator mechanisms. PSS effects may be expected also in the non-stretched limb possibly through an imbalance between the systemic hemodynamic control and the local vasodilator response. To this purpose, eight young healthy individuals (age: 22\ub13 yrs) underwent PSS (5 cycles of 45 s stretch/15 s rest) of the knee extensors of the dominant limb. Femoral artery blood velocity and diameter were taken from both limbs by ultrasound. FBF was then calculated. PSS increased FBF by 3c78% in the stretched limb (from 495\ub1110 to 882\ub1121 ml/min; P<0.05). FBF returned to baseline within the end of the 45 s stretch. Conversely, FBF decreased transitory by 3c71% (from 334\ub1155 to 138\ub117 ml/min; P<0.05) in the non-stretched limb during PSS maneuver. In conclusion, PSS increased FBF in the stretched limb, and induced a FBF decrease in the contralateral limb. These findings may suggest the predominance of a local vasodilator mechanism in the stretched limb during PSS maneuver, probably induced by nitric oxide release. On the contrary, a possible systemic vasoconstriction, likely mediated by an elevation of sympathetic nerve activity, may prevail in the contralateral limb