The Contractile Machines of the Heart.

This chapter will describe basic structural and functional features of the contractile apparatus of muscle cells of the heart, namely, cardiomyocytes and smooth muscle cells. Cardiomyocytes form the contractile myocardium of the heart, while smooth muscle cells form the contractile coronary vessels. Both muscle types have distinct properties and will be considered with respect to their cellular appearance (brick-like cross-striated versus spindle-like smooth), arrangement of contractile proteins (sarcomeric versus non-sarcomeric organization), calcium activation mechanisms (thin-filament versus thick-filament regulation), contractile features (fast and phasic versus slow and tonic), energy metabolism (high oxygen versus low oxygen demand), molecular motors (type II myosin isoenzymes with high adenosine diphosphate [ADP]-release rate versus myosin isoenzymes with low ADP-release rates), chemomechanical energy conversion (high adenosine triphosphate [ATP] consumption and short duty ratio versus low ATP consumption and high duty ratio of myosin II cross-bridges [XBs]), and excitation-contraction coupling (calcium-induced calcium release versus pharmacomechanical coupling). Part of the work has been published (Neuroscience - From Molecules to Behavior", Chap. 22, Galizia and Lledo eds 2013, Springer-Verlag; with kind permission from Springer Science + Business Media).

Home-based resistance training performed at either fast or slow speeds improves power output in older adults.

PURPOSE: We investigated the effect of an unsupervised, body mass- home-based resistance training program in older adults performed at either a fast or slow contractile speed on changes to muscle-power, -volume, -architecture, and fatigue resistance of the knee extensors. METHODS: Thirty-two male older adults (age 65-88 years) were separated into 1) fast-speed exercise (Fast-group), 2) slow-speed exercise (Slow-group), and 3) no exercise (Control-group) groups. Participants in the exercise groups performed 30-45 repetitions of knee-extension and sit-to-stand exercises 3 times a week for 8 weeks with different exercise speed between the groups. Before and after the intervention period, the following variables were measured: Isotonic power, isometric strength, twitch contractile properties, muscle-activity, -architecture, and -quality, neuromuscular fatigue resistance of the knee extensors, and thigh muscle volume. RESULTS: Peak power was increased in both the Fast-group (+24 %, P < 0.01, d = 0.65) and Slow-group (+12 %, P < 0.05, d = 0.33) but not in the Control-group. Training increased pennation angle of the vastus lateralis in both the Fast-group (+8 %, P < 0.01, d = 0.42) and Slow-group (+8 %, P < 0.01, d = 0.42), while only the Fast-group showed increase in pennation angle of the rectus femoris (+12 %, P < 0.01, d = 0.64) and thigh muscle volume (+16 %, P < 0.01, d = 0.52). There was no time × group interaction effect for the other neuromuscular measures. CONCLUSIONS: Unsupervised, body mass- and home-based resistance training performed at either fast or slow speeds can improve muscle power in older adults, while fast-speed exercise may be preferable over slow-speed owing to the relatively greater improvement of muscle-power, -volume, -architecture, and better time efficiency.

Attentional focus differentially modulates the corticospinal and intracortical excitability during dynamic and static exercise.

Although attentional focus affects motor performance, whether corticospinal excitability and intracortical modulations differ between focus strategies depending on the exercise patterns remains unclear. In the present study, using single- and paired-pulse transcranial magnetic stimulation and peripheral nerve stimulation, we demonstrated changes in the cortical and spinal excitability under external focus (EF) and internal focus (IF) conditions with dynamic or static exercise. Participants performed the ramp-and-hold contraction task of right index finger abduction against an object (sponge or wood) with both exercises. They were asked to concentrate on the pressure on the sponge/wood induced by finger abduction under the EF condition, and on the index finger itself under the IF condition. Motor-evoked potential (MEP) and F-wave in the premotor, phasic, or tonic phase, and short- and long-interval intracortical inhibition (SICI and LICI, respectively), and intracortical facilitation (ICF) in the premotor phase were examined by recording surface electromyographic activity in the right first dorsal interosseous muscle. Increments in the MEP amplitude were larger under the EF condition than under the IF condition in the dynamic, but not static, exercise. The F-wave, SICI, and LICI did not differ between focus conditions in both exercises. In the dynamic exercise, interestingly, ICF was greater under the EF condition than under the IF condition and positively correlated with the MEP amplitude. These results indicate that corticospinal excitability and intracortical modulations to attentional focus differ depending on exercise patterns, suggesting that attentional focus differentially affects the central nervous system responsible for diverse motor behaviors.NEW & NOTEWORTHY We investigated attentional focus-dependent corticospinal and intracortical modulations in dynamic or static exercise. The corticospinal excitability was modulated differentially depending on the focus of attention during dynamic, but not static exercise. Although the reduction of intracortical GABAergic inhibition was comparable between focus conditions in both exercises, intracortical facilitation was smaller when focusing on the internal environments in the dynamic exercise, resulting in lower activation of the corticospinal tract.

The effects of isokinetic training in athletes after knee surgery: a systematic review.

PURPOSE: To review the effectiveness of isokinetic training as an alternative method to traditional isotonic resistance training. MATERIALS AND METHODS: Researchers examined data from PubMed, CENTRAL, MEDLINE COMPLETE, and Web of Science until February 2023. A total of 365 entries were obtained from databases, including studies that analyzed the effects of isokinetic vs. isotonic-based rehabilitation in athletes (16-50 years) after a surgical knee intervention. Return to sport (RTS), strength of the flex/extensor compartment of the thigh, muscle mass of the thigh, and knee function were screened as main outcomes. Two reviewers independently screened the studies for eligibility and assessed the risk of bias of the included ones. RESULTS: Six studies involving 181 athletes were included. Isokinetic training demonstrated significant benefits in peak torque for knee flexor-extensor muscles in four studies. Two studies favored isokinetic training over isotonic for strength. Muscle mass findings were mixed, with one study favoring isokinetic significantly and two showing no significant differences. In terms of returning to sport, the isotonic group displayed slightly better limb symmetry index values, but without significance. Isokinetic training outperformed isotonic in two functionality questionnaire studies, while two others showed no significant differences. CONCLUSIONS: Isokinetic training appears equally, if not more effective than isotonic, for restoring strength balance between hamstrings and quadriceps. This could lead to more favorable muscle mass changes. Isokinetic training also parallels isotonic rehabilitation for functional outcomes and meeting return-to-sport criteria. Therefore, isokinetic training should be included as one of the main strength restoration strategies after knee surgery, especially in early and middle rehabilitation stages. REGISTRATION NUMBER: The present systematic review was registered on PROSPERO (registration number: CRD42022370398).

Trade-Off Between Maximal Power Output and Fatigue Resistance of the Knee Extensors for Older Men.

This study investigated associations of fatigue resistance determined by an exercise-induced decrease in neuromuscular power with prefatigue neuromuscular strength and power of the knee extensors in 31 older men (65-88 years). A fatigue task consisted of 50 consecutive maximal effort isotonic knee extensions (resistance: 20% of prefatigue isometric maximal voluntary contraction torque) over a 70° range of motion. The average of the peak power values calculated from the 46th to 50th contractions during the fatigue task was normalized to the prefatigue peak power value, which was defined as neuromuscular fatigue resistance. Neuromuscular fatigue resistance was negatively associated with prefatigue maximal power output (r = -.530) but not with prefatigue maximal voluntary contraction torque (r = -.252). This result highlights a trade-off between prefatigue maximal power output and neuromuscular fatigue resistance, implying that an improvement in maximal power output might have a negative impact on neuromuscular fatigue resistance.

The synergic effects of alpha-lipoic acid supplementation and electrical isotonic contraction on anthropometric measurements and the serum levels of VEGF, NO, sirtuin-1, and PGC1-α in obese people undergoing a weight loss diet.

Background: The anti-obesity effects of Alpha-lipoic acid (α-LA) and isotonic contraction has been reported. However, the underlying mechanism is not fully understood. This study aimed to investigate the effect of 1200 mg/day α-LA supplementation and 3 sessions per week of Faradic (an electrical stimulating system) on anthropometric parameters, body composition, VEGF, Sirtuin-1, nitric oxide (NO), and PGC1-α in obese people undergoing a weight loss regime.Methods: This randomised clinical trial was carried out on 100 obese adults. The subjects were randomly assigned to four groups of 25 subjects including Faradic, α-LA, α-LA + Faradic, and control. A Bio Impedance Analyser (BIA) was used to estimate anthropometric measurements including weight, body mass index (BMI), fat mass, and fat free mass. The serum levels of Sirtuin-1, PGC1-α, VEGF, and NO levels were measured. All measurements were done at baseline and after 8 weeks of the intervention.Results: A significant weight reduction was observed in all four groups compared to baseline (p<.01). The placebo group had significantly higher weight, BMI, weight circumstance (WC), and body fat (BF) compared with the other groups. The α-LA + Faradic group had significantly lower weight, BMI, BF, WC than control, faradic, and α-LA groups and higher, Sirtuin and PGC than the control group (all p < .05).Conclusions: The findings indicated that the α-LA and Faradic interventions may have a synergistic effect on weight, BMI, BF, WC, and SLM, possibly through changes in serum level of VEGF, NO, and PGC. Further studies are warranted to clarify the mutual effects of -α-LA and Faradic on obesity and its molecular mechanisms. Name of the registry: Iranian Registry of Clinical TrialsTrial registration number: IRCT20131117015424N2Date of registration: 04/04/2018URL of trial registry record: https://www.irct.ir/search/result?query=IRCT20131117015424N2.

A novel adaptable isometric strength analysis and exercise development system design.

In this study, a low-cost and adaptable isometric strength measurement and exercise development system are described. The implemented system consists of mechanical structure, force measurement sensor, electronic circuit, and computer software. Isometric-isotonic (via spring resistance) strength analysis and various exercise programs can be applied with the system. The developed system has a lower cost compared to its counterparts in the literature and has a structure that can be adapted to different machines and measuring methods. The operability and reliability of the isometric strength measurement and exercise development system have been proven by calibration tests.

Delayed onset muscle soreness intensity affects muscular performance / El Dolor muscular de aparición tardía afecta el desempeño muscular

Abstract Background: The study of functional impact of delayed onset muscle soreness has been limited to describe the decline on maximal isometric contraction, but muscular work and time to peak torque has not been examined yet. Purpose: To describe the changes induced by a session of lengthening contractions on muscle performance and delayed onset muscle soreness (DOMS). Methods: A quasi-experimental study was conducted in the Institutional laboratory; Twenty healthy men; mean age 21 SD 0.34 were recruited, all subjects performed 200 lengthening contractions of the quadriceps at 120°/s. Isometric and isokinetic peak torque, muscular work, time to peak torque, DOMS and creatine kinase activity were assessed at baseline, 48 h and 96 h post-exercise. The muscle performance was assessed with an isokinetic dynamometer and DOMS with a visual analog scale (VAS). Results: Relative to baseline, isometric and isokinetic peak torque and muscular work decreased in ~30% at 48 h post-exercise; delayed onset muscle soreness increased ~300%, which remained at 96 h post-exercise. Conclusions: These reflect that the decline in muscular performance is due to the changes in peak torque and muscular work, which has greater implications on muscle function. No changes were detected in time to peak torque. The alterations in muscular performance variables are accompanied by delayed onset muscle soreness which has also a negative impact on force production (29% of the drop on peak torque is explain by soreness intensity).

Resumen Introducción: Los estudios de impacto funcional del dolor muscular de aparición tardía (DMAT) se han limitado a describir la disminución de la contracción isométrica máxima, pero aún no se ha examinado el trabajo muscular y el tiempo del torque máximo. Objetivo: Describir los cambios inducidos por una sesión de ejercicio excéntrico sobre el rendimiento muscular y DMAT. Método: se realizó un estudio cuasi-experimental, los participantes fueron veinte hombres sanos; edad media 21 DE 0,34, todos los sujetos realizaron 200 contracciones excéntricas del cuádriceps a 120°/s. Se evaluó el torque pico isométrico e isocinético, el trabajo muscular, el tiempo hasta el torque máximo, DMAT y la actividad de la creatina quinasa al inicio, 48 h y 96 h después del ejercicio, el rendimiento muscular se evaluó con un dinamómetro isocinético y DOMS con una escala análoga visual (EAV). Resultados: en relación con la línea de base, el torque pico isométrico e isocinético y el trabajo muscular disminuyeron en ~ 30 % a las 48 h post-ejercicio; El dolor muscular de aparición tardía aumentó ~300 %, que permaneció 96 h después del ejercicio. Conclusiones: los resultados reflejan que la disminución del rendimiento muscular se debe a los cambios en el torque pico y trabajo muscular, lo que tiene mayores implicaciones en la función muscular. No se detectaron cambios en el tiempo hasta el torque máximo. Las alteraciones en las variables de rendimiento muscular se acompañan de DMAT que también tiene un impacto negativo en la producción de fuerza (el 29 % de la caída en el torque máximo se explica por la intensidad del dolor).

The effect of alpha-lipoic acid supplementation and electrical isotonic contraction on anthropometric parameters, body composition and angiogenesis factor, sirtunin-1 and peroxisome proliferator-activated receptor-γ coactivator-1α in obese people under a weight loss regime: A study protocol for a randomized controlled clinical trial.

BACKGROUND: Obesity is defined as a chronic disease, and is known as a public health problem in developed and developing countries. Several studies have shown the effects of anti-obesity of α-lactalbumin. AIM: This study was designed to investigate the effect of alpha-lipoic acid supplementation and electrical isotonic contraction on anthropometric parameters, body composition and angiogenesis factor, sirtunin-1 and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α) in obese people under a weight loss regime. METHODS: Obese people who meet the inclusion criteria are included. Participants are randomly divided into four groups (alpha-lipoic (1200 mg) +weight loss regime group; Faradic (three 1 hour sessions) + weight loss regime group; alpha-lipoic (1200 mg) + Faradic (three 1 hour sessions) + weight loss regime group; control group (1200 mg placebo) for 2 months. At the beginning and the end of the study, demographic information, dietary intake, anthropometric parameters, body composition and serum levels of the angiogenesis factor (sirtunin-1, PGC1α and nitric oxide) are measured. CONCLUSION: Recent studies reported the anti-obesity effects of alpha-lipoic acid. This study is novel, since a similar study has not yet been carried out. This study evaluates the effect of 600 mg of alpha-lipoic acid supplementation or having three sessions of 1 hour per week electrical isotonic contraction induced by Faradic for 2 months alone or in combination in obese people that are undergoing a weight loss regime. TRIAL REGISTRATION: Iran Clinical Trials Registry, ID: IRCT20131117015424N2. Registered 2018-04-02.

Differential contributions of fatigue-induced strength loss and slowing of angular velocity to power loss following repeated maximal shortening contractions.

The purpose of this study was to investigate the relationship between fatigue-induced reductions in isometric torque and isotonic power and to quantify the extent to which the decreases in angular velocity and dynamic torque can explain the power loss immediately following an isotonic fatiguing task and throughout recovery in seven young males and six young females. All measurements were performed with both legs. For dorsiflexion, fatigue-related time-course changes in isometric maximal voluntary contraction (MVC) torque, angular velocity, dynamic torque, and power production following repeated maximal isotonic contractions (load: 20% MVC) were investigated before, immediately after, and 1, 2, 5 and 10 min after a fatiguing task. There were no relationships between the fatigue-related reductions in isometric MVC torque and peak power at any timepoint, suggesting that fatigue-induced reductions in isometric MVC torque does not entirely reflect fatigue-induced changes in dynamic performance. The relative contribution of fatigue-related reduction in dynamic torque on power loss was greater immediately following the task, and lower throughout recovery than the corresponding decrease in angular velocity. Thus, power loss immediately following the task was more strongly related to the decline in dynamic torque; however, this relationship shifted throughout recovery to a greater dependence on slowing of angular velocity for power loss.

Analysis of Recruitment Pattern of Related Muscles in Two Types of Active Straight Leg Raise / 中国康复理论与实践

Objective:To compare the rate of recruitment in two types of active straight leg raise (ASLR) and to investigate the activation patterns of the related muscles. Methods:From June to October, 2018, eleven healthy subjects were recruited. Surface electromyography (sEMG) signals of unilateral rectus femoris, bilateral rectus abdominis, internal oblique abdominis, external oblique abdominis and multifidus were recorded in normal ASLR (Action A) and raising leg for ten seconds (Action B). %maximal voluntary isometric contraction (MVIC) of these muscles was processed and analyzed. Results:%MVIC of ipsilateral internal oblique muscle and external oblique muscle were greater than the opposite side (t > 2.549, P < 0.05) in Action A; %MVIC of ipsilateral internal oblique muscle, external oblique muscle and rectus abdominis muscle were greater than the opposite side (t > 2.240, P < 0.05) in Action B; compared with action B, Action A had higher %MVIC of bilateral internal oblique and rectus femoris (t > 3.549, P < 0.05). Conclusion:The activation mode of ipsilateral dominance was shown in both actions, and the different motion control strategies may be adopted by the neuromuscular system in different ASLR.

Mathematical model for isometric and isotonic muscle contractions.

A new mathematical model is presented to describe both the active and passive mechanics of muscles. In order to account for the active response, a two-layer kinematics that introduces both the visible and rest lengths of the muscle is presented within a rational mechanics framework. The formulation is based on an extended version of the principle of virtual power and the dissipation principle. By using an accurate constitutive description of muscle mobility under activation, details of microscopic processes that lead to muscle contraction are glossed over while macroscopic effects of chemical/electrical stimuli on muscle mechanics are retained. The model predictions are tested with isometric and isotonic experimental data collected from murine extensor digitorum muscle. It is shown that the proposed model captures experimental observations with only three scalar parameters.

Contractility of Right Ventricular Myocardium in Male and Female Rats during Physiological and Pathological Hypertrophy.

Sex differences in the morphogenesis and adaptation of the mechanisms controlling myocardium contractility during physiological and pathological hypertrophy of the right ventricle were demonstrated in mature rats. The study revealed sex-dependent effects of physiological and pathological cardiac hypertrophy on the coefficient of variation of the cardiomyocyte diameter, length-dependent control of the contractile force, and the maximum velocity of isotonic shortening.

Acute effect of different stretching methods on the strength performance in successive series / Efeito agudo de diferentes métodos de alongamento sobre o desempenho da força em séries sucessivas

ABSTRACT There is still no consensus about the use of stretching before strength exercises in successive series. Thus, the aim was to verify the acute effect of two stretching methods on the strength performance in the bench press exercise. Trained subjects performed 3 sets of 8 to10-RM in the bench press immediately after the static stretching (SS), Proprioceptive Neuromuscular Facilitation (PNF) or control condition. There was a significant decrease in repetitions in the second and third series compared to the first for all conditions. There was no significant difference in the number of repetitions or total volume between the conditions with and without stretching. The SS and PNF induced no negative effect on strength performance and can be used prior to this exercise

RESUMO Ainda não há consenso sobre a utilização de alongamentos antes de exercícios de força em séries sucessivas. Sendo assim, o objetivo foi verificar o efeito agudo de dois métodos de alongamento sobre o desempenho da força no exercício supino reto. Indivíduos treinados realizaram 3 séries de 8 a 10-RM no supino reto imediatamente após o alongamento estático (AE), Facilitação Neuromuscular Proprioceptiva (FNP) ou condição controle. Foi encontrada queda significativa das repetições na segunda e terceira séries em comparação à primeira em todas as condições. Não houve diferença significativa no número de repetições ou no volume total entre as condições com e sem alongamento. O AE e a FNP não causaram impacto negativo no desempenho da força, podendo, assim, serem utilizados previamente a esse exercício.

Reduction of contractility and reactivity in isolated lymphatics from hemorrhagic shock rats with resuscitation

PURPOSE: To evaluate the changes of contractility and reactivity in isolated lymphatics from hemorrhagic shock rats with resuscitation. METHODS: Six rats in the shock group suffered hypotension for 90 min by hemorrhage, and resuscitation with shed blood and equal ringer's solution. Then, the contractility of lymphatics, obtained from thoracic ducts in rats of the shock and sham groups, were evaluated with an isolated lymphatic perfusion system using the indices of contractile frequency (CF), tonic index (TI), contractile amplitude (CA) and fractional pump flow (FPF). The lymphatic reactivity to substance P (SP) was evaluated with the different volume of CF, CA, TI and FPF between pre- and post-treatment of SP at different concentrations. RESULTS: The CF, FPF, and TI of lymphatics obtained from the shocked rats were significantly decreased than that of the sham group. After SP stimulation, the ∆CF (1×10-8, 3×10-8, 1×10-7, 3×10-7 mol/L), ∆FPF (1×10-8, 3×10-8, 1×10-7 mol/L), and ∆TI (1×10-8 mol/L) of lymphatics in the shock group were also obviously lower compared with the sham group. In addition, there were no statistical differences in CA and ∆CA between two groups. CONCLUSION: Lymphatic contractility and reactivity to substance P appears reduction following hemorrhagic shock with resuscitation. .

Altered corticomuscular coherence elicited by paced isotonic contractions in individuals with cerebral palsy: a case-control study.

The purpose of the study was to analyze corticomuscular coherence during planning and execution of simple hand movements in individuals with cerebral palsy (CP) and healthy controls (HC). Fourteen individuals with CP and 15 HC performed voluntary paced movements (opening and closing the fist) in response to a warning signal. Simultaneous scalp EEG and surface EMG of extensor carpi radialis brevis were recorded during 15 isotonic contractions. Time-frequency corticomuscular coherence (EMG-C3/C4) before and during muscular contraction, as well as EMG intensity, onset latency and duration were analyzed. Although EMG intensity was similar in both groups, individuals with CP exhibited longer onset latency and increased duration of the muscular contraction than HC. CP also showed higher corticomuscular coherence in beta EEG band during both planning and execution of muscular contraction, as well as lower corticomuscular coherence in gamma EEG band at the beginning of the contraction as compared with HC. In conclusion, our results suggest that individuals with CP are characterized by an altered functional coupling between primary motor cortex and effector muscles during planning and execution of isotonic contractions. In addition, the usefulness of corticomuscular coherence as a research tool for exploring deficits in motor central processing in persons with early brain damage is discussed.

Isotonic resistance jaw exercise alters jaw muscle coordination during jaw movements.

The aim was to investigate the effects of isotonic resistance exercise on the electro-myographic (EMG) activity of the jaw muscles during standardised jaw movements. In 12 asymptomatic adults surface EMG activity was recorded from the anterior temporalis and masseter muscles bilaterally and the right anterior digastric muscle during right lateral jaw movements that tracked a target. Participants were randomly assigned to a Control group or an Exercise group. Jaw movement and EMG activity were collected (i) at baseline, before the exercise task (pre-exercise); (ii) immediately after the exercise task (isotonic resistance at 60% MVC against right lateral jaw movements); (iii) after 4 weeks of a home-based exercise programme; and, (iv) at 8-weeks follow-up. There were no significant within-subject or between-group differences in the velocity and amplitude of the right lateral jaw movements either within or between data collection sessions (P > 0.05). However, over the 8 weeks of the study, three of the tested EMG variables (EMG Duration, Time to Peak EMG from EMG Onset, and Time to Peak EMG activity relative to Movement Onset) showed significant (P < 0.05) differences in the five tested muscles. Many of the significant changes occurred in the Control group, while the Exercise group tended to maintain the majority of the tested variables at pre-exercise baseline values. The data suggest a level of variability between recording sessions in the recruitment patterns of some of the muscles of mastication for the production of the same right lateral jaw movement and that isotonic resistance exercise may reduce this variability.

Electromyographic analysis of upper limb muscles during standardized isotonic and isokinetic robotic exercise of spastic elbow in patients with stroke.

Although it has been reported that strengthening exercise in stroke patients is beneficial for their motor recovery, there is little evidence about which exercise method is the better option. The purpose of this study was to compare isotonic and isokinetic exercise by surface electromyography (EMG) analysis using standardized methods. Nine stroke patients performed three sets of isotonic elbow extensions at 30% of their maximal voluntary isometric torque followed by three sets of maximal isokinetic elbow extensions with standardization of mean angular velocity and the total amount of work for each matched set in two strengthening modes. All exercises were done by using 1-DoF planner robot to regulate exact resistive torque and speed. Surface electromyographic activity of eight muscles in the hemiplegic shoulder and elbow was recorded. Normalized root mean square (RMS) values and co-contraction index (CCI) were used for the analysis. The isokinetic mode was shown to activate the agonists of elbow extension more efficiently than the isotonic mode (normalized RMS for pooled triceps: 96.0±17.0 (2nd), 87.8±14.4 (3rd) in isokinetic, 80.9±11.0 (2nd), 81.6±12.4 (3rd) in isotonic contraction, F[1,8]=11.168; P=0.010) without increasing the co-contraction of muscle pairs, implicating spasticity or synergy.

Efeitos de contraceptivo hormonal oral sobre o grau de força e composição corporal de jogadoras de vôlei: um estudo piloto / Effects of oral hormonal contraceptive on the strength level and body composition of volleyball female players: a pilot study

Verificar os efeitos dos contraceptivos hormonais orais (CO) sobre o grau de força muscular e na composição corporal de mulheres jovens atletas. Participaram desse estudo 12 mulheres jovens adultas com idade superior a 18 anos, atletas amadoras de voleibol, que participavam ativamente de treinos e competições. A amostra foi divida em Grupo Contraceptivo (GCO, n=7) e Grupo Não Contraceptivo (GNCO, n=5). Foi aplicado um questionário sobre características sociodemográficas, comportamentais, de saúde e relacionadas ao treinamento. Realizaram-se medidas antropométricas, testes de força por dinamometria e de carga de uma repetição máxima. A análise dos dados foi realizada através da análise descritiva (média ± desvio padrão) e inferencial (teste t de Student não pareado ou teste de Wilcoxon não pareado) e o nível de significância aceito foi de p<0,05. Na escolha do CO como método contraceptivo, a maioria das atletas do grupo que GCO fazem uso de contraceptivos orais de terceira geração, fazem uso dos mesmo há pelo menos 5 anos e motivaram-se a usar o medicamento por sua eficiência e eficácia no controle de natalidade. As atletas do grupo GNCO utilizavam a camisinha como método contraceptivo. Em relação a composição corporal, as atletas do grupo GCO apresentaram medidas de dobras cutâneas, circunferência corporal, percentual de gordura e peso mais elevados do que as atletas do grupo GNCO, porém em nenhum dos grupos foi observado um percentual de gordura equivalente ou superior a 25%, valor considerado como na média para mulheres com idade entre 25 e 35 anos. Nenhuma das variáveis analisadas apresentou associação estatisticamente significativa com a ingestão de CO e alterações de força e performance atlética; apenas no valor da circunferência da coxa medial encontrou-se significativa limítrofe (p=0,05). No presente estudo, os COs não exerceram efeitos significantes sobre a força muscular e composição corporal de jovens atletas amadoras de voleibol.

The study aimed to evaluate potential effects of hormonal contraceptives (OC) on muscle strength and body composition in young female amateur volleyball players. Twelve women (18 or older) participated in the study, all of them were volleyball players, who were training and competing. The sample was divided into Contraceptive Group (OCG, n = 7) and Non Contraceptive Group (NOCG, n = 5). We administered a questionnaire on socio-demographic, behavioral, health-related information and training aspects. Anthropometric measurements, grip strength and maximum repetition tests were taken. Data analysis was performed with descriptive analysis (means ± standard deviations) and inferential statistics (Student's unpaired t test or Wilcoxon unpaired test) and the level of significance was set to 0.05. Among OC users, most athletes use third-generation oral contraceptives, for at least 5 years and were motivated to use the drug for their efficiency and effectiveness as a birth control method. The athletes from NOCG group used condoms as a contraceptive method. Regarding body composition, athletes from OCG group presented higher skinfolds, body circumference, body fat percentage and weight compared to athletes from NOCG group, but in none of the groups body fat was equal to or exceeded 25%, which is considered a value in average for women between the ages of 25 and 35. None of the analyzed variables showed any statistically significant association with oral contraceptives; only thigh’s circumference presented borderline significance (p=0.05). In this study, hormonal contraceptives did not exert significant effects on muscle strength and body composition of young amateur volleyball players.

The Effects of K(+) Channel Blockade on Eccentric and Isotonic Twitch and Fatiguing Contractions in situ.

K(+) channel blockers like 3,4-diaminopyridine (DAP) can double isometric muscle force. Functional movements require more complex concentric and eccentric contractions, however the effects of K(+) channel blockade on these types of contractions in situ are unknown. Extensor digitorum longus (EDL) muscles were stimulated in situ with and without DAP in anesthetized rats and fatigability was addressed using a series of either concentric or eccentric contractions. During isotonic protocols (5-100% load), DAP significantly shifted shortening- and maximum shortening velocity-load curves upward and to the right and increased power and work. Maximum shortening, maximum shortening velocity, and power doubled while work increased by ∼250% during isotonic contraction at 50% load. During isotonic fatigue, DAP significantly augmented maximum shortening, work, shortening velocity, and power. During constant velocity eccentric protocols (2-12 mm/s), DAP increased muscle force during eccentric contractions at 6, 8, 10, and 12 mm/s. During eccentric contraction at a constant velocity of 6 mm/s while varying the stimulation frequency, DAP significantly increased muscle force during 20, 40, and 70 Hz. The effects of DAP on muscle contractile performance during eccentric fatigue varied with level of fatigue. DAP-induced contractile increases during isotonic contractions were similar to those produced during previously studied isometric contractions, while the DAP effect during eccentric contractions was more modest. These findings are especially important in attempting to optimize functional electrical stimulation parameters for spinal cord injury patients while also preventing rapid fatigue of those muscles.