Electrical and mechanical response of finger flexor muscles during voluntary isometric contractions in elite rock-climbers

Effect of acute meal and long-term intake of a Mediterranean Diet providing different amounts of carbohydrates on physical performance and biomarkers in non-professional strength athletes

The study aims to evaluate the effect of an acute meal and long-term intake of Mediterranean Diet (MD) on different parameters such as strength, physical performance, body composition and blood markers in a group of non-professional athletes who practice a strength activity. Thirteen volunteers completed two 8-week dietary interventions in a randomised, cross-over design. Also an acute study was performed. Subjects received a MD High in carbohydrates, characterised by at least five portions of pasta/week and an average 55-60% of daily energy derived from carbohydrates, versus an MD reduced in carbohydrates, with less than two portions of pasta/week and an average of 40-45% of daily energy provided by carbohydrates. Mainly, data did not show significant differences for the parameters analysed, except for Elbow Flexor maximum voluntary contraction (p = .039). Results enlighten that increasing total carbohydrates intake, as typically in the MD, does not negatively affect physical performance, body composition and strength.

Persistent Unilateral Force Production Deficits Following Hand Injury in Experienced Climbers: A Reliability and Retrospective Injury Study

INTRODUCTION

In climbing, research is needed to guide clinical and training advice regarding strength differences between hands. The objectives of this study were to establish test-retest reliability of a field-based apparatus measuring sport-specific unilateral isometric hand strength and to investigate whether these measures detect between-hand differences in climbers with and without a history of unilateral hand injury.

METHODS

A reliability and case-control injury study was carried out. Seventeen intermediate-advanced climbers without and 15 intermediate-advanced climbers with previous unilateral hand injury participated. Unilateral isometric fingertip flexor strength was assessed during maximal voluntary contraction (MVC) and peak rate of force development (RFD) tests in full-crimp overhead position. The magnitude of within-group between-hand differences was calculated using a generalized estimating equation to evaluate if prior injury was associated with lower MVC and RFD outcomes and whether hand dominance influenced the magnitude of these effects. The control group was assessed 1 wk later to determine intraclass correlation coefficients (ICCs) for all measures.

RESULTS

The MVC (ICC 0.91-0.93) and the RFD (ICC 0.92-0.83) tests demonstrated moderate-to-high reliability. When accounting for handedness, those with prior injury showed 7% (P=0.004) reduced MVC and 13% (P=0.008) reduced RFD in the injured hand. The nondominant hand was also significantly weaker in MVC (11%, P<0.001) and RFD (12%, P=0.02) outcomes. For uninjured climbers, MVC and RFD were not significantly higher in the dominant hand (differing by 4% and 5%, respectively).

CONCLUSIONS

Previous climbing injury was associated with persistent weakness in the injured limb and exacerbated handedness effects. Therefore, recommendations for rehabilitation should be considered.

Indices reflecting muscle contraction performance during exercise based on a combined electromyography and mechanomyography approach

Electromyography (EMG) and mechanomyography (MMG) have been used to directly evaluate muscle function through the electromechanical aspect of muscle contraction. The purpose of this study was to establish new absolute indices to describe muscle contraction performance during dynamic exercise by combining EMG and displacement MMG (dMMG) measured simultaneously using our previously developed MMG/EMG hybrid transducer system. Study participants were eight healthy male non-athletes (controls) and eight male athletes. EMG and dMMG of the vastus medialis were measured for 30 s during four cycles of recumbent bicycle pedaling (30, 60, 90, and 120 W) and on passive joint movement. Total powers were calculated based on the time domain waveforms of both signals. Muscle contraction performance was verified with the slope of regression line (SRL) and the residual sum of squares (RSS) obtained from EMG and dMMG correlation. EMG and dMMG has increased with the work rate. Force and EMG were similar between groups, but dMMG showed a significant difference with load increase. Athletes had significantly higher SRL and significantly lower RSS than controls. The average value divided by SRL and RSS was higher in athletes than in controls. The indices presented by the combined approach of EMG and dMMG showed a clear contrast between the investigated groups and may be parameters that reflect muscle contraction performance during dynamic exercise.

Upper body rate of force development and maximal strength discriminates performance levels in sport climbing

The aim of this study was to assess and compare the maximal force and rate of force development (RFD) between intermediate, advanced and elite climbers using several different methods for calculating RFD. Fifty-seven male climbers (17 intermediate, 25 advanced, and 15 elite) performed isometric pull-ups on a climbing-specific hold while the RFD was calculated using several absolute (50, 100, 150, 200, and 250 ms from onset of force) and relative time periods (25, 50, 75, 95, and 100% of time to peak force). The maximal force was higher among elite climbers compared to advanced (ES = 1.78, p < 0.001) and intermediate climbers (ES = 1.77, p < 0.001), while no difference was observed between intermediate and advanced climbers (P = 0.898). The elite group also showed higher RFD than the other two groups at all relative time periods (ES = 1.02-1.58, p < 0.001-0.002), whereas the absolute time periods only revealed differences between the elite vs. the other groups at 50, 100 and 150 ms from the onset of force (ES = 0.72-0.84, p = 0.032-0.040). No differences in RFD were observed between the intermediate and advanced groups at any time period (p = 0.942-1.000). Maximal force and RFD, especially calculated using the longer periods of the force curve, may be used to distinguish elite climbers from advanced and intermediate climbers. The authors suggest using relative rather than absolute time periods when analyzing the RFD of climbers.

Comparison of Grip Strength in Recreational Climbers and Non-Climbing Athletes-A Cross-Sectional Study

In recent years, climbing sports is on the rise making its Olympic debut in 2021. Physiological traits of professional rock climbers have been intensively studied, while recreational indoor climbers are less investigated, especially regarding grip strength and upper extremity proportions. In this cross-sectional study, we aimed to understand what discerns the recreational climber from disparate recreational athletes. Therefore, we analyzed 50 recreational climbing (30.3 ± 12.7 years, 1.76 ± 0.09 m and 67.0 ± 14.0 kg) and 50 non-climbing athletes (26.4 ± 9.1 years, 1.78 ± 0.09 m and 73.2 ± 12.6 kg) to detect differences in their finger grip strength of seven different pinches. In addition, the upper extremity proportions were measured. Even in recreational climbers, almost all analyzed grips were stronger compared to other athletes (p < 0.05 in all but non-dominant fist, small to moderate effect sizes). Only the grip strength of the whole non-dominant hand was not significantly different (p = 0.17). Interestingly, differences between the dominant and non-dominant hand appeared to be larger in the non-climbing (all p < 0.05, all but one with small effect size) compared to the climbing cohort (pinch I/IV and pinch I/II+III+IV not different and mostly trivial). Circumference measurements showed that 10 cm below the lateral epicondyle, climbers exhibited significantly greater perimeter compared to non-climbing athletes (p < 0.05, small effect size). Our results show that recreational climbers have higher measured grip strength, but less profound differences between the dominant and non-dominant hand.

Reduced Neuromuscular Performance in Night Shift Orthopedic Nurses: New Insights From a Combined Electromyographic and Force Signals Approach

The effect of sleep–wake rhythm disruption on neuromuscular control and muscle fatigue has received little attention. Because nurse shift work is so varied, including overnight duty, rotating shift schedules, early awakening, and interrupted nocturnal sleep, it offers an interesting model to study this paradigm. It has been investigated so far using only subjective markers. A combined approach based on the simultaneous analysis of surface electromyographic (sEMG) and force signals can objectively detect possible deficits in neuromuscular control and muscle fatigue. With this study we investigated neuromuscular activation and muscle contraction capacity at submaximum and maximum level in nurses working two night-shift schedules and compared them to levels in nurses working entirely in day shifts. Sleep quality and activity levels were also assessed. The study sample was 71 nurses grouped by their shift work schedule: night shift for 5 days (NS₅, n = 46), night shift for 10 days (NS₁₀, n = 9), and only day/swing shift (DS, n = 16). Before and after the shift-work cycle, maximum voluntary contraction (MVC) force and muscle activation, neuromuscular control, and muscle fatigability were measured in the finger flexor muscles. Activity level and sleep quality during the shift-work cycle were recorded with a wrist actigraph. After the shift-work cycles, MVC force and muscle activation were decreased (−11 ± 3% and −33 ± 3%, p < 0.001) as was neuromuscular control (−36 ± 8%, p = 0.007), whereas muscle fatigability was increased (+ 19 ± 9%, p = 0.006) in the NS₅ and the NS₁₀ group. Sleep quality was lower in the NS₅ and the NS₁₀ group (−8 ± 1.8% and −15%3, respectively, p < 0.001), while the activity level for the three groups was similar. There was a clear reduction in neuromuscular control and an increase in muscle fatigue in the nurses working the night shift. These findings may inform of work schedule planning or recommendations for devising new recovery strategies to counteract neuromuscular alterations in night shift nurses.

Comparison of climbing-specific strength and endurance between lead and boulder climbers

Albeit differences in climbing-specific strength of the forearms have been demonstrated between lead and boulder climbers, little is known about the potential differences in force and power output of the upper body pulling-apparatus between disciplines. The aim of this study was to compare the climbing-specific upper-body strength and finger flexor endurance between lead and boulder climbers, as well as to examine the relative utilization of force when testing on a ledge hold compared to a jug hold. Sixteen boulder climbers (red-point climbing grade 17.9 ± 3.3) and fifteen lead climbers (red-point climbing grade 20.5 ± 3.5) performing on an advanced level volunteered for the study. Peak force, average force and rate of force development (RFD) were measured during an isometric pull-up, average velocity in dynamic pull-up, and finger flexor endurance in an intermittent test to fatigue. The isometric pull-up was performed on a ledge hold (high finger strength requirements) and on a jug hold (very low finger strength requirements). Boulder climbers demonstrated a higher maximal and explosive strength in all strength and power measurements (26.2–52.9%, ES = 0.90–1.12, p = 0.006–0.023), whereas the finger flexor endurance test showed no significant difference between the groups (p = 0.088). Both groups were able to utilize 57–69% of peak force, average force and RFD in the ledge condition compared to the jug condition, but the relative utilization was not different between the groups (p = 0.290–0.996). In conclusion, boulder climbers were stronger and more explosive compared to lead climbers, whereas no differences in finger flexor endurance were observed. Performing climbing-specific tests on a smaller hold appears to limit the force and power output equally between the two groups.

Determinants for success in climbing: A systematic review

Background

The number of athletes engaged in climbing sports has risen. Specific physical and psychological skills are required. The objective of this review was to determine factors for high climbing performance. We evaluated physiological, biomechanical and psychological characteristics that simplify the ascent. We also assessed training and recovery strategies.

Methods

Medline (Pubmed), Cochrane Library and Google scholar up to September 2018.

Results

A low skinfold thickness, body fat and large forearm volume were anthropometric traits in successful climbers. Well-trained forearm flexors with high aerobic capacities lead to an efficient style. Hand grip strength and endurance, postural stability and optimized kinematic motions were favourable. Elite climbers had long finger and bent-arm hang times. Psychologically, an “iceberg profile” was typical. Constant training with fingerboard and dynamic eccentric-concentric training helped to push the “red-point grade”.

Conclusion

Hand, forearm strength and endurance are highly important elements in elite climbers. An efficient climbing style with perpetual focus and accuracy, high speed and low exhaustion due to adaption to repeated isometric exercise is helpful in the ascent, while low body fat and a large bone-to-tip pulp make it easier. Constant training is essential, e.g. eccentric-concentric training of finger flexors, which should be followed by active recovery.

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Physiological parameters of high climbing performance are forearm flexor strength and a good strength-to-weight ratio.

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An efficient climbing style is based on perpetual focus, accuracy and a high postural stability.

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With constant training, especially isometric exercise, followed by active recovery, climbing red-point grade can be improved.

Surface mechanomyography and electromyography provide non-invasive indices of inspiratory muscle force and activation in healthy subjects

The current gold standard assessment of human inspiratory muscle function involves using invasive measures of transdiaphragmatic pressure (Pdi) or crural diaphragm electromyography (oesEMGdi). Mechanomyography is a non-invasive measure of muscle vibration associated with muscle contraction. Surface electromyogram and mechanomyogram, recorded transcutaneously using sensors placed over the lower intercostal spaces (sEMGlic and sMMGlic respectively), have been proposed to provide non-invasive indices of inspiratory muscle activation, but have not been directly compared to gold standard Pdi and oesEMGdi measures during voluntary respiratory manoeuvres. To validate the non-invasive techniques, the relationships between Pdi and sMMGlic, and between oesEMGdi and sEMGlic were measured simultaneously in 12 healthy subjects during an incremental inspiratory threshold loading protocol. Myographic signals were analysed using fixed sample entropy (fSampEn), which is less influenced by cardiac artefacts than conventional root mean square. Strong correlations were observed between: mean Pdi and mean fSampEn |sMMGlic| (left, 0.76; right, 0.81), the time-integrals of the Pdi and fSampEn |sMMGlic| (left, 0.78; right, 0.83), and mean fSampEn oesEMGdi and mean fSampEn sEMGlic (left, 0.84; right, 0.83). These findings suggest that sMMGlic and sEMGlic could provide useful non-invasive alternatives to Pdi and oesEMGdi for the assessment of inspiratory muscle function in health and disease.

The effects of different durations of static stretching within a comprehensive warm-up on voluntary and evoked contractile properties

Evidence for performance decrements following prolonged static stretching (SS) has led to a paradigm shift in stretching routines within a warm-up. Rather than SS, dynamic stretching (DS) and dynamic activity (DA) have replaced SS within warm-up routines. The objective of the present study was to compare the effect of differing lower limb SS durations (30 [SS30s], 60 [SS60s] or 120 s [SS120s] of SS per muscle group or no-stretch control) within a comprehensive warm-up protocol consisting of aerobic activity, DS and DA. Sixteen male participants completed the four stretching conditions in a randomized order, after a 5-min low-intensity (cycle) warm-up and before a DS/DA component on separate days. Tests included passive hip and knee ranges of motion (ROM), maximum voluntary knee extensor/flexor force, force produced at 100 ms (F100), vertical jump height and evoked knee extensor contractile properties. For hip flexion (hamstrings) ROM, SS120s provided the largest increase (5.6-11.7%) followed by SS60s (4.3-11.4%), control (4.4-10.6%) and SS30s (3.6-11.1%). For knee flexion (quadriceps) ROM, SS30s provided the largest increase (9.3-18.2%) followed by SS120s (6.5-16.3%), SS60s (7.2-15.2%) and control (6.3-15.2%). There were decreases in quadriceps F100 following SS in SS120s (29.6%) only. There were increases in vertical jump performance in the control (6.2%), SS60s (4.6%) and SS30s (3.3%). While 120 s SS per muscle increased ROM, even within a comprehensive warm-up routine, it also elicited notable performance decrements. However, moderate durations of SS were observed to improve ROM whilst either having negligible or beneficial (but not detrimental) effects on specific aspects of athletic performance.

Correlation between stiffness and electromechanical delay components during muscle contraction and relaxation before and after static stretching

The study was aimed at assessing possible correlations of the electromechanical delay components during muscle contraction (Delay_TOT) and relaxation (R-Delay_TOT), with muscle-tendon unit (MTU), muscle, and tendon stiffness before and after static stretching (SS). Plantarflexor muscles' maximum voluntary torque (T_max) was measured in 18 male participants (age 24±3yrs; body mass 76.4±8.9kg; stature 1.78±0.09m; mean±SD). During T_max, surface electromyogram (EMG), mechanomyogram, and force signals were detected. Delay_TOT and R-Delay_TOT with their electrochemical and mechanical components were calculated. Passive torque and myotendinous junction displacement were assessed at 0°, 10° and 20° of dorsiflexion to determine MTU, muscle and tendon stiffness. The same protocol was repeated after SS. Delay_TOT, R-Delay_TOT and their mainly mechanical components correlated with MTU, muscle and tendon stiffness, both before (R² from 0.562 to 0.894; p<0.001) and after SS (R² from 0.726 to 0.955; p<0.001). SS decreased T_max (-14%; p<0.001) and lengthened almost all the Delay_TOT and R-Delay_TOT components (from +5.9% to +30.5%; p<0.05). Correlations were found only between stiffness and the mechanical components of Delay_TOT and R-Delay_TOT. Correlations persisted after SS but delays increased to a higher extent than stiffness, indicating a complexity of the relationship between stiffness and delays that will be discussed in the manuscript.

Higher Neuromuscular Manifestations of Fatigue in Dynamic than Isometric Pull-Up Tasks in Rock Climbers

Neuromuscular assessment of rock climbers has been mainly focused on forearm muscles in the literature. We aimed to extend the body of knowledge investigating on two other upper limb muscles during sport-specific activities in nine male rock climbers. We assessed neuromuscular manifestations of fatigue recording surface electromyographic signals from brachioradialis and teres major muscles, using multi-channel electrode arrays. Participants performed two tasks until volitional exhaustion: a sequence of dynamic pull-ups and an isometric contraction sustaining the body at half-way of a pull-up (with the elbows flexed at 90°). The tasks were performed in randomized order with 10 minutes of rest in between. The normalized rate of change of muscle fiber conduction velocity was calculated as the index of fatigue. The time-to-task failure was significantly shorter in the dynamic (31 ±10 s) than isometric contraction (59 ±19 s). The rate of decrease of muscle fiber conduction velocity was found steeper in the dynamic than isometric task both in brachioradialis (isometric: −0.2 ±0.1%/s; dynamic: −1.2 ±0.6%/s) and teres major muscles (isometric: −0.4±0.3%/s; dynamic: −1.8±0.7%/s). The main finding was that a sequence of dynamic pull-ups lead to higher fatigue than sustaining the body weight in an isometric condition at half-way of a pull-up. Furthermore, we confirmed the possibility to properly record physiological CV estimates from two muscles, which had never been studied before in rock climbing, in highly dynamic contractions.

Motor unit activation strategy during a sustained isometric contraction of finger flexor muscles in elite climbers

The aim of the study was to evaluate, by an electromyographic (EMG) and mechanomyographic (MMG) combined approach, whether years of specific climbing activity induced neuromuscular changes towards performances related to a functional prevalence of fast resistant or fast fatigable motor units. For this purpose, after the maximum voluntary contraction (MVC) assessment, 11 elite climbers and 10 controls performed an exhaustive handgrip isometric effort at 80% MVC. Force, EMG and MMG signals were recorded from the finger flexor muscles during contraction. Time and frequency domain analysis of EMG and MMG signals was performed. In climbers: (i) MVC was higher (762 ± 34 vs 512 ± 57 N; effect size: 1.64; confidence interval: 0.65-2.63; P < 0.05); (ii) endurance time at 80% MVC was 43% longer (34.2 ± 3.7 vs 22.3 ± 1.5 s; effect size: 1.21; confidence interval: 0.28-2.14; P < 0.05); (iii) force accuracy and stability were greater during contraction (P < 0.05); (iv) EMG and MMG parameters were higher throughout the entire isometric effort (P < 0.05). Collectively, force, EMG and MMG combined analysis revealed that several years of specific climbing activity addressed the motor control system to adopt muscle activation strategies based on the functional prevalence of fast resistant motor units.

Torque and mechanomyogram correlations during muscle relaxation: effects of fatigue and time-course of recovery

To assess the validity and reliability of the mechanomyogram (MMG) as a tool to investigate the fatigue-induced changes in the muscle during relaxation, the torque and MMG signals from the gastrocnemius medialis muscle of 23 participants were recorded during tetanic electrically-elicited contractions before and immediately after fatigue, as well as at min 2 and 7 of recovery. The peak torque (pT), contraction time (CT) and relaxation time (RT), and the acceleration of force development (d2RFD) and relaxation (d2RFR) were calculated. The slope and τ of force relaxation were also determined. MMG peak-to-peak was assessed during contraction (MMG p-p) and relaxation (R-MMG p-p). After fatigue, pT, d2RFD, d2RFR, slope, MMG p-p and R-MMG p-p decreased significantly, while CT, RT and τ increased (P < 0.05 for all comparisons), remaining altered throughout the entire recovery period. R-MMG p-p correlated with pT, MMG p-p, slope, τ and d2RFR both before and after fatigue. Reliability measurements always ranged from high to very high. In conclusion, MMG may represent a valid and reliable index to monitor the fatigue-induced changes in muscle mechanical behavior, and could be therefore considered an effective alternative to the force signal, also during relaxation.

Coordination of respiratory muscles assessed by means of nonlinear forecasting of demodulated myographic signals

Pulmonary diseases such as obstructive sleep apnea syndrome (OSAS) affect function of respiratory muscles. Individuals with OSAS suffer intermittent collapse of the upper airways during sleep due to unbalanced forces generated by the contraction of the diaphragm and upper airway dilator muscles. Respiratory rhythm and pattern generation can be described via nonlinear or coupled oscillators; therefore, the resulting activation of different respiratory muscles may be related to complex nonlinear interactions. The aims of this work were: to evaluate locally linear models for fitting and prediction of demodulated myographic signals from respiratory muscles; and to analyze quantitatively the influence of a pulmonary disease on this nonlinear forecasting related to low and moderate levels of respiratory effort. Electromyographic and mechanomyographic signals from three respiratory muscles (genioglossus, sternomastoid and diaphragm) were recorded in OSAS patients and controls while awake during an increased respiratory effort. Variables related to auto and cross prediction between muscles were calculated from the r(2) coefficient and the estimation of residuals, as functions of prediction horizon. In general, prediction improved linearly with higher levels of effort. A better prediction between muscle activities was obtained in OSAS patients when using genioglossus as the predictor signal. The prediction was significant for more than two respiratory cycles in OSAS patients compared to only a half cycle in controls. It could be concluded that nonlinear forecasting applied to genioglossus coupling with other muscles provides a promising assessment to monitor pulmonary diseases.