Muscle Contractile Properties Research Articles

Effects of Eccentric Single-Leg Decline Squat Training Performed With Different Execution Times on Maximal Strength and Muscle Contraction Properties of the Knee Extensor Muscles.

Abián-Vicén, J, Martínez, F, Jiménez, F, and Abián, P. Effects of eccentric single-leg decline squat training performed with different execution times on maximal strength and muscle contraction properties of the knee extensor muscles. J Strength Cond Res 36(11): 3040-3047, 2022-The eccentric phase of the single-leg decline squat (SLDS e ) has been described as a method to maximally load the knee extensor and has been used as an easy and effective rehabilitation exercise for patellar tendinopathy. The purpose of this study was to examine the impact of 6-week SLDS e training with 2 technical execution times on changes related to strength and muscle contractile properties. Thirty-six healthy volunteers were randomly divided into 3 groups: a control group (CG, n = 13, no training), a slow training group ( n = 11, SLDS e in 6 seconds), and a fast training group ( n = 12, SLDS e in 3 seconds). Subjects completed a 6-week SLDS e training program (80% of eccentric one repetation maximum [1RM]) 3 days a week. Pre, post, and 6-week follow-up of maximal dynamic and isometric strength and muscle contractile properties were assessed. After 6 weeks, training maximal loads showed a significant increase ( p < 0.05) in 1RM of the SLDS e (∼92-95%), the concentric peak torque at 180°·s -1 (∼38%) and 60°·s -1 (∼25%), and the extension isometric peak torque (∼12%), with no differences between both experimental groups. Moreover, a decrease ( p < 0.05) was found in the contraction time of the vastus medialis (VM) and the response time of the 3 analyzed quadriceps muscles. After the 6-week detraining period, there was a decrease in strength in all tests and in both experimental groups (1RM = 28-37%, isometric and isokinetic tests = 7-17%) and all contractile properties returned to baseline, except for the response time of the vastus lateralis in the fast training group and the contraction time of the VM in the STG. In conclusion, the SLDS e training protocol produced significant increases in muscle strength, showing important neuromuscular changes regardless of the technical execution time. It was also found that the training reduced the response and contraction time of the knee extensor musculature.

Acute Capsaicin and Exercise Performance in Humans: Potential Neuromuscular Mechanisms

The pungent bioactive ingredient in peppers (Capsaicin; CAP) has been widely investigated for its activation of the transient receptor potential vanilloid 1 (TRPV1) channel on sensory neurons. It has been shown to improve mitochondrial biogenesis, adenosine triphosphate (ATP) production and vascular function. In animal models has been demonstrated that increases exercise performance and decreases fatigue development. However, whether acute oral CAP improves endurance performance and the potential underlying mechanisms remains elusive. This study aimed to evaluate the potential ergogenic and anti-fatigue effects of acute oral CAP supplementation in healthy humans. In a double-blind, placebo-controlled, cross-over design, 10 young healthy males performed constant-load cycling exercise (294±55W; 85% of peak power output) to exhaustion, after acute ingestion of placebo (PL; 1000mg fiber pill) and CAP (780mg pill) capsules. Fatigue was assessed on the dominant quadriceps with the interpolated twitch technique, via changes in supramaximal electrical stimulation pre- vs. post-exercise, during isometric maximal voluntary contractions (MVC) and at rest. Cardiopulmonary parameters (heart rate, cardiac output, oxygen consumption, ventilation) were assessed throughout the exercise. No statistically significant differences were detected in the muscle contractile functions, despite a trend (P=0.07) for a decreased time to exhaustion during CAP (PL: 369±85 vs. CAP: 296±64 sec). All the values (except muscle voluntary activation (%VMA)) significantly decreased from pre- to post-exercise in both conditions. The exercise-induced attenuation of the intrinsic muscle contractile properties (Maximal rate of force development (MRFD) and Maximal relaxation rate (MRR) of the resting twitch force) were mitigated, in part, by CAP. Notably, in the PL condition MRR was seemingly reduced by 47±33%, while only of 29±68% in CAP; contrarily, MRFD decreased similarly of 47±23% and of 40±27% in PL and CAP, respectively. In 9 participants, the resting twitch (estimate of peripheral muscle fatigue) pre- vs. post-exercise decreased less with CAP (PL: 44±17 vs. CAP: 37±13%). CAP did not influence the MVC nor %VMA. The cardiopulmonary responses were similar between the conditions (P>0.05). In contrast to prior work, acute oral capsaicin did not improve endurance performance in the present study. CAP did elicit a tendency for faster relaxation rate, which might suggest an enhanced activation of the sarcoendoplasmic reticulum calcium ATPase (SERCA) pumps, thereby increasing the rate of Ca2+ reuptake and relaxation. However, this altered Ca2+ handling might also increase ATP demand. The tendency for CAP to attenuate the exercise-induced reduction in muscle function, or fatigue, might provide a mechanistic basis for the previously demonstrated beneficial effects of CAP. Further work is needed in larger samples, to further determine the optimal dosing and loading strategies, to better understand the potential ergogenic effects of capsaicin.

Tensiomyographic changes of muscle contractile properties in individuals with lower-limb amputation: A pilot study.

Individuals with a unilateral lower-limb amputation (LLA) rely heavily on their intact limb during daily physical activities. However, there is limited research on the resultant effects of this over-reliance on contractile properties of muscles in the intact limb. To compare the muscle contractile properties of the intact limb among individuals with a unilateral LLA to those of age-matched able-bodied individuals, using tensiomyography. This is a cross-sectional, observational study. Nine men with a unilateral LLA and 10 able-bodied men (control) were included. Tensiomyography measures were obtained for 5 muscles: gastrocnemius lateralis (GL) and medialis (GM), rectus femoris, vastus lateralis (VL), and vastus medialis. Contraction time (Tc), delay time (Td), maximal displacement (Dm), and velocity of deformation (Vd) for each muscle were compared between groups. Tc and Td for the GL and GM muscles were lower for the LLA than the control group (GL: P = .03, r = -0.51, P < .01, r = 0.67; GM: P = .02, r = 0.53, P = .07, r = 0.54, respectively). Dm and Vd of the VL were significantly smaller in the LLA than the control group (P < .01, r = 0.73, P < .01, r = 0.23, respectively). Men with a unilateral LLA seem to have slower deformation of the gastrocnemius muscles and higher stiffness of the VL than able-bodied controls. These findings may be indicative of an overuse of the intact limb as a compensation for the unilateral LLA. The confirmation of these findings in a larger sample size is required to translate these findings to practice.

Quercetin ingestion modifies human motor unit firing patterns and muscle contractile properties

Quercetin is a polyphenolic flavonoid that has reported to block the binding of adenosine to A1 receptors at central nervous system and increase calcium release from the sarcoplasmic reticulum at skeletal muscle. The aim of the present study was to investigate the acute effect of quercetin ingestion on motor unit activation and muscle contractile properties. High-density surface electromyography during submaximal contractions and electrically elicited contraction torque in knee extensor muscles were measured before (PRE) and 60 min after (POST) quercetin glycosides or placebo ingestions in 13 young males. Individual motor units of the vastus lateralis muscle were identified from high-density surface electromyography by the Convolution Kernel Compensation technique. Firing rates of motor units recruited at 30–50% of the maximal voluntary contraction torque (MVC) were increased from PRE to POST only with quercetin (9.0 ± 2.3 to 10.5 ± 2.0 pps, p = 0.034). Twitch torque during doublet stimulation was decreased from PRE to POST with placebo (77.1 ± 17.1 to 73.9 ± 17.6 Nm, p = 0.005), but not with quercetin (p > 0.05). For motor units recruited at < 10% of MVC, normalized firing rate were decreased with quercetin (1.52 ± 0.33 to 1.58 ± 0.35%MVC/pps, p = 0.002) but increased with placebo (1.61 ± 0.32 to 1.57 ± 0.31%MVC/pps, p = 0.005). These results suggest that ingested quercetin has the functional roles to: mitigate reduction in the muscle contractile properties, enhance activations of relatively higher recruitment threshold motor units, and inhibit activation of relatively lower recruitment threshold motor units.

Ubiquitin Ligases at the Heart of Skeletal Muscle Atrophy Control.

Skeletal muscle loss is a detrimental side-effect of numerous chronic diseases that dramatically increases mortality and morbidity. The alteration of protein homeostasis is generally due to increased protein breakdown while, protein synthesis may also be down-regulated. The ubiquitin proteasome system (UPS) is a master regulator of skeletal muscle that impacts muscle contractile properties and metabolism through multiple levers like signaling pathways, contractile apparatus degradation, etc. Among the different actors of the UPS, the E3 ubiquitin ligases specifically target key proteins for either degradation or activity modulation, thus controlling both pro-anabolic or pro-catabolic factors. The atrogenes MuRF1/TRIM63 and MAFbx/Atrogin-1 encode for key E3 ligases that target contractile proteins and key actors of protein synthesis respectively. However, several other E3 ligases are involved upstream in the atrophy program, from signal transduction control to modulation of energy balance. Controlling E3 ligases activity is thus a tempting approach for preserving muscle mass. While indirect modulation of E3 ligases may prove beneficial in some situations of muscle atrophy, some drugs directly inhibiting their activity have started to appear. This review summarizes the main signaling pathways involved in muscle atrophy and the E3 ligases implicated, but also the molecules potentially usable for future therapies.

Effect of muscle stimulation intensity on the heterogeneous function of regions within an architecturally complex muscle.

Skeletal muscle has fiber architectures ranging from simple to complex, alongside variations in fiber-type and neuro-anatomical compartmentalization. However, the functional implications of muscle subdivision into discrete functional units remain poorly understood. The rat medial gastrocnemius has well-characterized regions with distinct architectures and fiber type composition. Here, force-length and force-velocity contractions were performed for two stimulation intensities (supramaximal and submaximal) and for three structural units (whole muscle belly, proximal region, and distal region) to assess the effect of muscle compartmentalization on contractile force-length-velocity relationships and optimal speed for power production. Additionally, fiber strain, fiber rotation, pennation, and architectural gearing were quantified. Our results suggest that the proximal and distal muscle regions have fundamentally different physiological function. During supramaximal activation, the proximal region has shorter (8.4 ± 0.8 mm versus 10.9 ± 0.7 mm) fibers and steeper (28.7 ± 11.0° versus 19.6 ± 6.3°) fiber angles at optimum length, and operates over a larger (17.9 ± 3.8% versus 12.6 ± 2.7%) range of its force-length curve. The proximal region also exhibits larger changes in pennation angle (5.6 ± 2.2°/mm versus 2.4 ± 1.5°/mm muscle shortening) and architectural gearing (1.82 ± 0.53 versus 1.25 ± 0.24), whereas the distal region exhibits greater peak shortening speed (96.0 mm/s versus 81.3 mm/s) and 18-27% greater optimal speed. Overall, similar patterns were observed during submaximal activation. These regional differences in physiological function with respect to the whole muscle highlight how variation in motor recruitment could fundamentally shift regional functional patterns within a single muscle, which likely has important implications for whole muscle force and work output in vivo.NEW & NOTEWORTHY We show that muscle compartmentalization can influence whole muscle contractile properties, with slower-fibered proximal rat medial gastrocnemius undergoing larger changes in pennation angle and architectural gearing, whereas the faster-fibered distal region achieves greater peak and optimal shortening velocity, and power output. Consequently, regional variation in motor recruitment can fundamentally influence functional patterns within a single muscle.

Thermal robustness of biomechanical processes

Temperature influences many physiological processes that govern life as a result of the thermal sensitivity of chemical reactions. The repeated evolution of endothermy and widespread behavioral thermoregulation in animals highlight the importance of elevating tissue temperature to increase the rate of chemical processes. Yet, movement performance that is robust to changes in body temperature has been observed in numerous species. This thermally robust performance appears exceptional in light of the well-documented effects of temperature on muscle contractile properties, including shortening velocity, force, power and work. Here, we propose that the thermal robustness of movements in which mechanical processes replace or augment chemical processes is a general feature of any organismal system, spanning kingdoms. The use of recoiling elastic structures to power movement in place of direct muscle shortening is one of the most thoroughly studied mechanical processes; using these studies as a basis, we outline an analytical framework for detecting thermal robustness, relying on the comparison of temperature coefficients (Q 10 values) between chemical and mechanical processes. We then highlight other biomechanical systems in which thermally robust performance that arises from mechanical processes may be identified using this framework. Studying diverse movements in the context of temperature will both reveal mechanisms underlying performance and allow the prediction of changes in performance in response to a changing thermal environment, thus deepening our understanding of the thermal ecology of many organisms.

AN ASSESSMENT OF THE CONTRACTILE PROPERTIES OF THE SHOULDER MUSCULATURE IN ELITE VOLLEYBALL PLAYERS USING TENSIOMYOGRAPHY.

In volleyball, offensive (Hitters) and defensive players (Non-Hitters) perform differing actions that vary both kinematically and in terms of intensity. This may impose contrasting demands on the musculature involved in performing these actions. Previous research has identified differences in the muscle activation and contractile properties of the lower-body musculature between positions. Additionally, asymmetries between dominant and non-dominant limbs of the upper-body musculature has been observed in athletes performing overhead movements. The aim of this study was to use Tensiomyography (TMG) to examine the contractile properties of the shoulder musculature in elite volleyball players. Cross-sectional study. Thirty-one elite volleyball players participated in this study (Age: 23 ± 2 yrs, Body Mass: 76.5 ± 9.8 kg, Stature: 181 ± 9.3 cm), 26 of which displayed right-limb dominance and five displayed left-limb dominance. Contractile properties of the shoulder musculature including the anterior deltoid (AD), biceps brachii (BB), posterior deltoid (PD), and the upper trapezius (UT) were assessed bilaterally using TMG measures on one occasion prior to any training or exercise. The contractile measures provided by TMG included the maximal displacement (Dm), contraction time (Tc), delay time (Td), sustain time (Ts), and the relaxation time (Tr). No statistically significant differences were observed between positions or limbs, except that Hitters displayed a significantly lower Ts of the left AD compared to Non-hitters (p = 0.01, ES = 1.02), and significant differences between dominant and non-dominant sides in the Td of the UT in Non-hitters were present (p = 0.05, ES = 0.8). These data suggest that irrespective of playing position and limb dominance, contractile properties of the shoulder musculature in elite volleyball players, as measured using TMG, display few significant differences. 3b.

Six weeks of localized heat therapy does not affect muscle mass, strength and contractile properties in healthy active humans.

Animal and human studies have shown that repeated heating may induce skeletal muscle adaptations, increasing muscle strength. The aim of this study is to investigate the effect of 6weeks of localized heating on skeletal muscle strength, volume and contractile properties in healthy humans. Fifteen active participants (8 males/7 females, 35 ± 6 years, 70 ± 14kg, 173 ± 7cm, average training of 87min per week) were subjected to 6weeks of single-leg heat therapy. Heat pads were applied for 8h/day, 5days/week, on one randomly selected calf of each participant, while the contralateral leg acted as control. The heat pads increased muscle temperature by 4.6 ± 1.2°C (p < 0.001). Every 2weeks, participants were tested for morphological (MRI), architectural (ultrasound), contractile (electrically evoked twitch), and force (isometric and isokinetic) adaptations. Repeated localized heating did not affect the cross-sectional area (p = 0.873) or pennation angle (p = 0.345) of the gastrocnemius muscles; did not change the evoked peak twitch amplitude (p = 0.574) or rate of torque development (p = 0.770) of the plantar flexors; and did not change maximal voluntary isometric (p = 0.214) or isokinetic (p = 0.973) plantar flexor torque. Whereas previous studies have observed improved skeletal muscle function following whole-body and localized heating in active and immobilized humans, respectively, the current data suggested that localized heating may not be a potent stimulus for muscle adaptations in active humans.

Novel perspective on contractile properties and intensity-dependent verification of force-frequency relationship during neuromuscular electrical stimulation.

Purpose The aims of the present study were: (a) to examine the effect of the stimulus intensity on force‐frequency and torque fluctuation–frequency relationships during Neuromuscular electrical stimulation; and (b) to identify a novel parameter that can be used to evaluate muscle contractile properties. Methods: Electrically elicited joint torque involving the quadriceps femoris muscle was recorded during neuromuscular electrical stimulation at two different stimulus intensities in 19 healthy men. Stimulation frequencies were set at 5–40 Hz with a duration of 10 s. Evoked joint torque was compared among all stimulation frequencies between the two stimulus intensities (68 and 113 V). The torque fluctuation at each stimulation frequency as the change in the contraction pattern was also compared between the intensities. Torque and torque fluctuation were normalized at each frequency by the largest torque or torque fluctuation, respectively. We extracted a novel parameter: the arrival point of tetanic contraction based on force‐frequency and torque fluctuation‐frequency curves. Results: There were significant differences in normalized torque at 5–25 and 40 Hz and in normalized torque fluctuation at 15–30 and 40 Hz between the two stimulus intensities. Extracted parameters showed no significant difference between the intensities. Conclusion: The results suggest that force–frequency relationships during neuromuscular electrical stimulation are influenced by the intensity of stimulation applied to the quadriceps femoris muscle. However, we consider that it is possible to simultaneously evaluate contractile properties using the novel parameter.

Effect of Three Half-Squat Protocols on the Tensiomyographic Twitch Response and Tissue Damage of the Rectus Femoris and the Biceps Femoris.

The aim of this study was to analyse the acute effects of a concentric exercise and two different eccentric overload exercises (EOEs) on blood markers of muscle damage (i.e. creatine kinase [CK], lactate dehydrogenase [LDH], myoglobin [Myo], and malondialdehyde [MDA]) and muscle contractile properties. Ten healthy, young (27 ± 1.5 years, 179 ± 6 cm, 78.7 ± 10.8 kg), physically active men (3.5 ± 1.9 h·w-1) randomly performed three training sessions using the following protocols: a half-squat (HS) as a concentric exercise, and exercises using Versapulley (VP) or YoYo isoinertial technology (YIT) as EOEs (4 x 7 repetitions with a 2 min rest interval between sets). Blood samples and tensiomyography measurements were obtained after each training session. Repeated measures analysis of variance (ANOVA) followed by the Tukey test was used to detect differences between the four time points of each variable. The standardized difference or effect size (ES, 90% confidence limit) in the selected variables was calculated using the basal SD. After all exercises, a greater activity of CK, LDH, and concentration of Myo, and MDA were found compared to baseline values (p < 0.05). A substantially greater activity of CK, LDH, and Myo concentration, but not MDA, were found after EOEs when compared to the HS protocol. Substantially lower tensiomyography results in the rectus femoris (RF) were reported, irrespective of the exercise mode performed. Also, no substantial differences were obtained in the biceps femoris (BF) between EOEs and the HS protocol. Time of contraction (Tc) in the RF was possibly to very likely lower in the HS in comparison to EOEs. Additionally, muscular displacement (Dm) in the RF was substantially lower in the HS compared to EOEs. VP produced higher concentrations of damage markers than YIT and concentric exercise did. Furthermore, tensiomyography variables showed similar activation in both exercises, although higher specific fatigue (in the RF) was registered in the traditional HS.

MUSCLE FUNCTION & HOMEOSTASIS / MOLECULAR THERAPEUTIC APPROACHES: P.76 Validation of in vivo and ex vivo readouts in a murine model of hind limb unloading to optimize translational research on skeletal muscle atrophy

Skeletal muscle atrophy is a major consequence of several pathophysiological conditions, including neuromuscular diseases, disuse (limb immobilization, space flight), aging (sarcopenia) and other wasting conditions (i.e. cancer cachexia). Basically, a disequilibrium between anabolic/catabolic pathways leads to progressive loss of muscle mass and functional impairment. The aim of translational research in this field is to identify anabolic compounds able to support protein synthesis and muscle mass, restoring muscle function and metabolism. Therefore, the validation of adequate readout parameters to assess atrophy and efficacy of therapeutics in reliable animal models is pivotal. Here, we focused on a detailed preclinical investigation of the hind limb unloading (HU) murine model, in which disuse leads to severe atrophy, dysfunction and damage in postural soleus (SOL) muscle. 10-week-old, male C57BL/6J mice underwent a 2-week HU protocol (T0–T2), in comparison to age-, sex-matched non-HU mice for a wide array of in vivo/ex vivo outcomes. At T0 (pre-HU), all mice had comparable body weight (BW). At T2, HU mice BW was significantly lower with respect to T0 (-9.7%) and to non-HU mice (-17.3%). We disclosed for the first time that in vivo torque of hind limb plantar flexor muscles (i.e. SOL, gastrocnemius) was severely impaired in HU mice, as well as SOL muscle contractile and elastic properties, measured ex vivo. This was paralleled by a significant decrease in SOL muscle mass (-39%) and total protein content (-47%). SOL muscle histology was also seriously compromised by HU protocol, with clear signs of myofiber damage and atrophy (significant decrease in fiber cross-sectional area vs non-HU condition). Finally, we found a remarkable -61% reduction of salivary IgA levels, which suggests a HU-induced negative immune response modulation, in line with previous observations from other models of hind limb suspension. Overall, our findings support the usefulness of the HU mouse model for preclinical translational research on skeletal muscle atrophy.

The effect of swimming training on adrenomedullin levels, oxidative stress variables, and gastrocnemius muscle contractile properties in hypertensive rats

ABSTRACT Introduction/Aim: Regular exercise may have beneficial effects on high blood-pressure, as shown in different types of experimental hypertension models in rats. The present study aims to investigate the effects of 6-week swimming training on blood pressure, oxidative stress variables of selected tissues, serum adrenomedullin (ADM) levels, and in situ muscle contraction in rats with hypertension induced by Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME), an inhibitor of endothelial nitric oxide synthases (eNOs). Materials and Methods: Twenty-six male Sprague Dawley, 8 weeks of age, rats were randomly divided into four groups: (I) normotensive (C), (II) normotensive + exercise (E), (III) hypertensive (L), and (IV) hypertensive + exercise (LE). Hypertension was induced by the oral administration of L-NAME (60 mg/kg) for 6 weeks. Exercise was performed 5 times (1-h each) per week for 6 weeks. At the end of the experiment, blood and tissue samples (the gastrocnemius muscle, heart, kidney, and thoracic aorta) were collected following contractile properties of the gastrocnemius muscle in situ weredetermined. In the collected tissues, oxidative stress (e.g., lipid oxidation and antioxidant enzyme activity) and serum ADM levels were measured. 6-week L-NAME administration per se (Group L) led to a significant increase in systolic and diastolic blood pressure compared to other groups. Results: Importantly, 6-week exercise caused a protective effect of high blood pressure in the rats received L-NAME (Group LE). The level of ADM was lower in the rats received L-NAME than that of the control group. L-NAME increased lipid peroxidation in the thoracic aorta and decreased superoxide dismutase in the heart, kidney and muscle, and decreased catalase and glutathione in the heart. However, the exercise intervention did not have protective effect on the L-NAME-mediated oxidative damage in the collected tissues. Conclusion: In conclusion, 6-week exercise intervention rescued rats from high blood pressure, but did not have ameliorative effect on the decreased ADM levels.

Local knee heating increases spinal and supraspinal excitability and enhances plantar flexion and dorsiflexion torque production of the ankle in older adults.

Aging is associated with progressive loss of active muscle mass and consequent decreases in resting metabolic rate and body temperature, and slowing of nerve conduction velocities and muscle contractility. These effectors compromise the ability of the elderly to maintain an upright posture during sudden balance perturbation, increase the risk of falls, and lead to self-imposed reduction in physical activity. Short-term superficial acute heating can modulate the neural drive transmission to exercising muscles without any marked change in deep-muscle temperature. To determine whether the short-term (5min) application of local passive knee-surface heating (next-to-skin temperature, ~ 44°C) in healthy older subjects of both sexes (64-74years; eight men/eight women) enhances reflex excitability, we compared the voluntarily and electrically induced ankle muscle torque production and contractile properties with those of healthy younger subjects of both sexes (21-35years, 10 men/10 women). The application of local heating (vs. control) increased the maximal Hoffman reflex (Hmax), the maximal volitional wave (Vsup) amplitude, and the Hmax/Mmax amplitude ratio, and decreased Vsup latency only in older adults. In the older adults (vs. younger adults), the application of local heating (vs. control trial) was accompanied by a significant increase in maximal voluntary peak torque, rate of torque development, and isokinetic peak torque of plantar flexion/dorsiflexion muscle contraction. The spinal and supraspinal reflex excitability of older adults increased during local knee-heating application. The improved motor drive transmission observed in older adults was accompanied by increased voluntarily induced torque production of the ankle muscles during isometric/isokinetic contractions.

Muscle contractile properties of cancer patients receiving chemotherapy: Assessment of feasibility and exercise effects.

BackgroundThis pilot trial explores the feasibility of measuring muscle contractile properties in patients with cancer, effects of exercise during chemotherapy on muscle contractile properties and the association between changes in contractile muscle properties and perceived fatigue.MethodPatients who received (neo)adjuvant chemotherapy for breast or colon cancer were randomized to a 9‐12 week exercise intervention or a waitlist‐control group. At baseline and follow‐up, we measured knee extensor strength using maximal voluntary contraction (MVC), contractile muscle properties of the quadriceps muscle using electrical stimulation, and perceived fatigue using the Multidimensional Fatigue Inventory. Feasibility was assessed by the proportion of patients who successfully completed measurements of contractile muscle properties. Exercise effects on muscle contractile properties were explored using linear regression analyses. Between‐group differences >10% were considered potentially relevant. Pearson correlation (r p) of changes in contractile muscle properties and changes in perceived fatigue was calculated.ResultsTwenty two of 30 patients completed baseline and follow‐up assessments. Measurements of contractile properties were feasible except for muscle fatigability. We found a potentially relevant between‐group difference in the rate of force development favoring the intervention group (1192 N/s, 95% CI = −335; 2739). Change in rate of force development was negatively correlated with change in perceived general (r p = −0.54, P = .04) and physical (r p = −0.59, P = .02) fatigue.ConclusionChemotherapy induces a decrease in the rate of force development, which may reflect a larger loss in type II muscle fibers. This may be attenuated with (resistance) exercise. The increase in the rate of force development was related to a decrease in perceived fatigue.

Is Low-Frequency Electrical Stimulation a Tool for Recovery after a Water Rescue? A Cross-Over Study with Lifeguards.

This study aimed to evaluate the degree to which transcutaneous electrical stimulation (ES) enhanced recovery following a simulated water rescue. Twenty-six lifeguards participated in this study. The rescue consisted of swimming 100 m with fins and rescue-tube: 50 m swim approach and 50 m tow-in a simulated victim. Blood lactate clearance, rated perceived effort (RPE), and muscle contractile properties were evaluated at baseline, after the water rescue, and after ES or passive-recovery control condition (PR) protocol. Tensiomiography, RPE, and blood lactate basal levels indicated equivalence between both groups. There was no change in tensiomiography from pre to post-recovery and no difference between recovery protocols. Overall-RPE, legs-RPE and arms-RPE after ES (mean ± SD; 2.7 ± 1.53, 2.65 ± 1.66, and 2.30 ± 1.84, respectively) were moderately lower than after PR (3.57 ± 2.4, 3.71 ± 2.43, and 3.29 ± 1.79, respectively) (p = 0.016, p = 0.010, p = 0.028, respectively). There was a significantly lower blood lactate level after recovery in ES than in PR (mean ± SD; 4.77 ± 1.86 mmol·L−1 vs. 6.27 ± 3.69 mmol·L−1; p = 0.045). Low-frequency ES immediately after a water rescue is an effective recovery strategy to clear out blood lactate concentration.

Influence of artificial turf temperature on physical performance and muscle contractile properties in football players after a repeated-sprint ability test

This study aimed to analyse the effect of playing surface temperature on muscular and thermal response to a repeated-sprint ability (RSA) test in football players. Thirty-two male football players (23 ± 5 years; 1.77 ± 0.06 m; 71.2 ± 6.7 kg) from two squads of a third-division football club participated in the study. An RSA test was carried out at a high surface temperature (45.34 ± 2.53 °C) and low surface temperature (27.21 ± 2.17 °C). Before and after this test, the muscular response of the players was assessed through tensiomyography and thermograms. The results revealed that performance in the RSA test particularly increased at a higher surface temperature, especially in the first 5 m of the 30 m sprint test. While a reduction in maximal radial displacement (Dm) in the biceps femoris post-RSA was observed at lower surface temperatures, a higher temperature on the thigh, hamstring and calf was found in the higher surface temperature group. In conclusion, higher surface temperatures had an influence on players’ thermal and tensiomyographic profile and improved performance in their repeated-sprint ability. These results suggest a need for coaches and players to be aware of these parameters to ensure adequate functionality and safety of the playing surface.

Intramuscular adipose tissue: a cause for concern.

Intramuscular adipose tissue: a cause for concern.

Greater fatigability and motor unit discharge variability in human type 2 diabetes.

This study determined the discharge characteristics of motor units from two lower limb muscles before and after fatiguing exercise in people with type 2 diabetes (T2D) with no symptoms of polyneuropathy and activity‐matched controls. Seventeen people with T2D (65.0 ± 5.6 years; 8 women) and 17 controls (63.6 ± 4.5 years; 8 women) performed: (a) intermittent, isometric contractions at 50% maximal voluntary isometric contraction (MVIC) sustained to failure with the ankle dorsiflexors, and (b) a dynamic fatiguing task (30% MVIC load) for 6 min with the knee extensors. Before and after the fatiguing tasks, motor unit characteristics (including coefficient of variation (CV) of interspike intervals (ISI)) were quantified from high‐density electromyography and muscle contractile properties were assessed via electrical stimulation. Fatigability was ~50% greater for people with T2D than controls for the dorsiflexors (time‐to‐failure: 7.3 ± 4.1 vs. 14.3 ± 9.1 min, p = .010) and knee extensors (power reduction: 56.7 ± 11.9 vs. 31.5 ± 25.5%, p < .001). The CV of ISI was greater for the T2D than control group for the tibialis anterior (23.1 ± 11.0 vs. 21.3 ± 10.7%, p < .001) and vastus lateralis (27.8 ± 20.2 vs. 24.5 ± 16.1%, p = .011), but these differences did not change after the fatiguing exercises. People with T2D had greater reductions in the electrically evoked twitch amplitude of the dorsiflexors (8.5 ± 5.1 vs. 4.0 ± 3.4%·min‐1, p = .013) and knee extensors (49.1 ± 10.0 vs. 31.8 ± 15.9%, p = .004) than controls. Although motor unit activity was more variable in people with T2D than controls, the greater fatigability of the T2D group for lower limb muscles was due to mechanisms involving disruption of contractile function of the exercising muscles rather than motor unit behavior.

Sports Injury Model For Effective Prevention, Diagnostic And Rehabilitation

In order to develop a model for a safe and effective return to sport after injuries, it is important to identify the risk factors associated with the occurrence of an injury. For the first time, we introduce the Tensiomyography (TMG) in the field of sport injuries (SI), a non-invasive and selective tool for the assessment of skeletal muscle contractile properties. As a recommendation from former experiences, a FC Barcelona documented a Muscle Injuries Clinical Guide 3.0 that explicitly emphasizes the use of TMG for the follow-up of muscle functional recovery and to help decide when the athlete can return to play. PURPOSE: To develop a thigh SI prediction model and explore factors of safe return to play. METHODS: The ongoing research project aims to monitor SI epidemiology in Slovenian premium soccer clubs. We monitored TMG of vastus lateralis and medialis, rectus femoris, biceps femoris and semitendinosus of both legs; body characteristics (body height, mass and fat), motor tasks (strength endurance in hamstrings; explosive lower-body strength, flexibility of lower body). RESULTS: Based on 11 thigh SI we were able to predict four (sensitivity 27%, specificity 99%). When predicting only 6 biceps femoris hamstring SI we could predict 4 (sensitivity 80%, specificity 100%). The predictive factors were derived only from TMG parameters. It appears that the worst-case scenario for the SI occurrence of biceps femoris is it short TMG-derived contraction time, high biceps femoris tone and low lateral symmetry. Interestingly, there were no significant predictors from body characteristics and motor tasks. CONCLUSION: Twenty-seven percent of all thigh SI and 80% of hamstring SI could be predicted solely from simple-to-use and non-invasive TMG screening. It seems that short contraction time (previously linked to high proportion of type II muscle fibers) and high muscle tone are risk factor for hamstring injuries, especially where imbalances between both lateral sides were present. Supported by Slovenian Research Agency (research core funding no. L5-8245).