Higher Percentage Of Fast-twitch Fibers Research Articles

The effects of multiple factors on post-activation potentiation and performance enhancement: a narrative review

Purpose: The aim of this review was to examine the effects of various factors, including recovery time, conditioning activity, range of motion, gender, age, fiber type percentage, training experience, and supplement intake, on post-activation potentiation (PAP) and post-activation performance enhancement (PAPE). After clarifying the differences between these two potentiation strategies, the review examines the physiological mechanisms underlying these processes and their relationship with the aforementioned factors. Methods: A literature search was conducted in multiple databases, using as keywords those factors, PAP and PAPE. Results: PAP/PAPE appears to benefit athletes, adults, and individuals with a higher percentage of fast-twitch fibers more. To increase performance, it is recommended to use an intensity greater than 80% of one repetition maximum and high volumes. For trained subjects, a recovery time of 3 to 10 minutes is beneficial, while its effectiveness for untrained subjects is still unclear. Potentiation is greater when the primer exercise has a wide range of motion and is similar to the verification test. Additionally, supplementation with caffeine or creatine also contributes to the magnitude of potentiation. Finally, although there is evidence suggesting a net potentiation, the balance between fatigue and potentiation remains complex and unclear. Conclusions: Each factor that interacts with PAP and PAPE should be evaluated individually to ensure the most appropriate conditioning activity for the athlete.

Muscle fiber typology substantially influences time to recover from high-intensity exercise.

Human fast-twitch muscle fibers generate high power in a short amount of time but are easily fatigued, whereas slow-twitch fibers are more fatigue resistant. The transfer of this knowledge to coaching is hampered by the invasive nature of the current evaluation of muscle typology by biopsies. Therefore, a noninvasive method was developed to estimate muscle typology through proton magnetic resonance spectroscopy in the gastrocnemius. The aim of this study was to investigate whether male subjects with an a priori-determined fast typology (FT) are characterized by a more pronounced Wingate exercise-induced fatigue and delayed recovery compared with subjects with a slow typology (ST). Ten subjects with an estimated higher percentage of fast-twitch fibers and 10 subjects with an estimated higher percentage of slow-twitch fibers underwent the test protocol, consisting of three 30-s all-out Wingate tests. Recovery of knee extension torque was evaluated by maximal voluntary contraction combined with electrical stimulation up to 5 h after the Wingate tests. Although both groups delivered the same mean power across all Wingates, the power drop was higher in the FT group (-61%) compared with the ST group (-41%). The torque at maximal voluntary contraction had fully recovered in the ST group after 20 min, whereas the FT group had not yet recovered 5 h into recovery. This noninvasive estimation of muscle typology can predict the extent of fatigue and time to recover following repeated all-out exercise and may have applications as a tool to individualize training and recovery cycles.NEW & NOTEWORTHY A one-fits-all training regime is present in most sports, though the same training implies different stimuli in athletes with a distinct muscle typology. Individualization of training based on this muscle typology might be important to optimize performance and to lower the risk for accumulated fatigue and potentially injury. When conducting research, one should keep in mind that the muscle typology of participants influences the severity of fatigue and might therefore impact the results.

O treinamento físico aeróbio corrige a rarefação capilar e as alterações nas proporções dos tipos de fibra muscular esquelética em ratos espontaneamente hipertensos

O treinamento físico (TF) aeróbio tem sido utilizado como um importante tratamento não farmacológico na hipertensão arterial (HA), uma vez que ele reduz a pressão arterial. Estudos mostram que as anormalidades do músculo esquelético na HA estão associados à rarefação capilar, um aumento na porcentagem de fibras de contração rápida (tipo II), com predominância do metabolismo glicolítico e um aumento da fadiga muscular. Entretanto, pouco se conhece sobre os efeitos do TF sobre estes parâmetros na HA. Nós hipotetizamos que o TF corrija a rarefação capilar potencialmente contribuindo para a restauração da proporção dos tipos de fibras musculares. Ratos espontaneamente hipertensos (SHR, n=14) e Wistar Kyoto (WKY, n=14) com 12 semanas de vida e divididos em 4 grupos: SHR, SHR treinado (SHR-T), WKY e WKY treinado (WKY-T) foram estudados. Como esperado, 10 semanas de TF foi efetivo em reduzir a pressão arterial em SHR-T. Além disso, avaliamos os principais marcadores de TF. A bradicardia de repouso, o aumento da tolerância a realização de esforço, do consumo de oxigênio de pico e da atividade da enzima citrato sintase muscular nos grupos de animais treinados (WKY-T e SHR-T) mostram que a condição aeróbia foi alcançada com este TF. O TF também corrigiu a rarefação capilar no músculo sóleo em SHR-T. Em paralelo, foi observada uma redução na porcentagem de fibras do tipo IIA e IIX, ao passo que aumentou a porcentagem de fibras do tipo I induzidas pelo TF na HA. Estes resultados sugerem que o TF previne as alterações na composição dos tipos de fibras no músculo sóleo em SHR, uma vez que a angiogênese e o aumento da atividade da enzima citrato sintase são umas das mais importantes adaptações ao TF aeróbio, atuando na manutenção do metabolismo oxidativo e do perfil de fibras do músculo.

Muscle strain injury: diagnosis and treatment.

Muscle strain is a very common injury. Muscles that are frequently involved cross two joints, act mainly in an eccentric fashion, and contain a high percentage of fast-twitch fibers. Muscle strain usually causes acute pain and occurs during strenuous activity. In most cases, the diagnosis can be made on the basis of the history and physical examination. Magnetic resonance imaging is recommended only when radiologic evaluation is necessary for diagnosis. Initial treatment consists of rest, ice, compression, and nonsteroidal anti-inflammatory drug therapy. As pain and swelling subside, physical therapy should be initiated to restore flexibility and strength. Avoiding excessive fatigue and performing adequate warm-up before intense exercise may help to prevent muscle strain injury. The long-term outcome after muscle strain injury is usually excellent, and complications are few.

Heredity of muscle fiber composition and correlated response of the synergistic muscle in rats.

The extent to which muscle fiber composition was determined by genes transmitted from parents and the correlated response of the synergistic muscle were analysed by using successive selection of rats. The foundation population (G0) was prepared by random choice from heterogeneous stock produced by random mating of three strains, Wistar-Imamichi, Fischer 344, and Donryu. Selective mating for a high percentage of fast-twitch fibers (%FT) in the deep portion of the lateral head of the gastrocnemius muscle and random mating were made from G0 to the seventh generation (G7). Successive selection caused a significant increase (P < 0.05) of %FT in the gastrocnemius muscle. The realized heritability for seven generations was 0.29. %FT in the soleus muscle of the selected line also increased (P < 0.05). In addition, significantly positive correlations (P < 0.05) were found between %FT in the gastrocnemius and soleus muscles in G1-G7. We conclude that approximately 29% of the variation of %FT was determined by genes transmitted from parents, and %FT in the gastrocnemius muscle was positively correlated with that of the soleus muscle.

Muscle Mechanics

Based on the MHC isoform pattern, adult mammalian limb skeletal muscles contain two and, in some species, three types of fast fibers (Type IIa, IIx, and IIb), and one slow fiber (Type I). Slow muscles, such as the soleus, contain primarily the slow Type I fiber, whereas fast-twitch muscles are composed primarily of a mixture of the fast myosin isozymes. Force generation involves cross-bridge interaction and transition from a weakly bound, low-force state (AM-ADP-P(i)) to the strongly bound, high-force state (AM-ADP). This transition is thought to be rate limiting in terms of dP/dt, and the high-force state is the dominant cross-bridge form during a peak isometric contraction. Intact fast and slow skeletal muscles generate approximately the same amount of peak force (Po) of between 200 and 250 kN.m-2. However, the rate of transition from the low- to high-force state shows Ca2+ sensitivity and is 7-fold higher in fast-twitch, as compared to slow-twitch, skeletal muscle fibers. Fiber Vo or the maximal cross-bridge cycle rate is highly correlated with and thought to be dependent on the specific activity of the myosin or myofibrillar ATPase. The hierarchy for Vo is the Type IIb > IIx > IIa > I. This functional difference for the fast fiber types explains the higher Vo observed in the predominantly Type IIb SVL vs. the mixed fast Type IIa and IIb EDL muscle. A plot of Vo vs. species size demonstrates that an inverse relationship exists between Vo and body mass. From the standpoint of work capacity, the important property is power output. An analysis of individual muscles indicates that peak power is obtained at loads considerably below 50% of Po. Individuals with a high percentage of fast-twitch fibers generate a greater torque and higher power at a given velocity than those with predominantly slow-twitch fibers. In humans, mean peak power occurred in a ratio of 10:5:1 for the Type IIb, IIa, and I fibers. The in vivo measurement of the torque-velocity relationship and Vmax in human muscle is difficult because of limitations inherent in the equipment used and the inability to study the large limb muscles independently. Nevertheless, the in vivo torque-velocity relationships are similar to those measured in vitro in animals. This observation suggests that little central nervous system inhibition exists and that healthy subjects are able to achieve maximal activation of their muscles. Although peak isometric tension is not dependent on fiber type distribution, a positive correlation exists between the percentage of fast fibers and peak torque output at moderate-to-high angular isokinetic velocities. Consequently, peak power output is substantially greater in subjects possessing a predominance of fast fibers. The mechanical properties of slow and fast muscles do adapt to programs of regular exercise. Endurance exercise training has been shown to increase the Vo of the slow soleus by 20%. This increase could have been caused by either a small increase in all, or most, of the fibers, or to a conversion of a few fibers from slow to fast. Recently, the increase was shown to be caused by the former, as the individual slow Type I fibers of the soleus showed a 20% increase in Vo, but there was little or no change in the percentage of fast fibers. The increased Vo was correlated with, and likely caused by, an increased fiber ATPase. We hypothesize that the increased ATPase and cross-bridge cycling speed might be attributable to an increased expression of fast MLCs in the slow Type I fibers (Fig. 14.10). This hypothesis is based on the fact that light chains have been shown to be involved in the power stroke, and removal of light chains depresses force and velocity. Regular endurance exercise training had no effect on fiber size, but with prolonged durations of daily training it depressed Po and peak power. When the training is maintained over prolonged periods, it may even induce atrophy of the slow Type I and fast Type IIa fibers. (ABSTRACT TRUNCATED)

Heterogeneity of Muscle Energetics in Human Muscle Fiber Type Using 31P Nuclear Magnetic Resonance

To evaluate the association between muscular phosphate metabolites or intracellular pH at rest and muscle fiber composition of musculus vastus lateralis in human, we measured phosphorus nuclear magnetic resonance (31P NMR) spectra and performed muscle biopsy in 30 subjects. The intracellular pH tended to be higher in cases with a higher percentage of fast-twitch fibers (% FT fibers). On the other hand, no relationship was observed between phosphocreatine (PCr)/inorganic phosphate (Pi) and percent FT fibers. This is inconsistent with previously reported results of 31P NMR studies in animals. These results suggest that PCr concentration is the same for the two major fiber types (FT and slow-twitch [ST] fibers) of human skeletal muscle. Knowledge of which relationship between muscle fiber composition and intracellular pH accounts for our results awaits further investigation.