Efeito dos diferentes percentuais de carga de treinamento (40% e 80% de 1 repetição máxima) utilizados em exercícios resistidos até falha concêntrica em indivíduos fisicamente ativos : estudo clínico controlado randomizado

Abstract

The scientific community recognizes muscle strength as an important component of physical fitness related to the improvement and maintenance of health. In this context, the training proposed to gain muscle strength is of great interest to health professionals and researchers. There are several ways to develop muscle strength, resistance training being the most common. Among the various methods of resistance training, the method of resistance training to concentric failure is becoming more popular every day. However, concentric failure is a multifactorial phenomenon, not yet fully elucidated by the scientific method. Thus, the aim of study 1 was to compare the effect of different training intensities to concentric failure, 80% vs. 40% repetition maximum (RM), on muscle adaptations in physically active individuals. A randomized controlled clinical trial was conducted with male subjects. Sixty participants were allocated three groups. The first group performed the training protocol with training load intensity of 40%MR. (G40, n=20); the second, a training with 80% RM (G80, n=20) and the third, control group (CG, n=20), did not perform any intervention. For groups G40 and G80 a training program was applied with resisted exercises for knee extensors and flexors until concentric failure, lasting eight weeks and three times a week, with a minimum interval of 48 hours between sessions. The order of the training was exercises in the Leg Press, the extensor chair, and the flexor table performed in the Exercise Clinic of the Universidade Vale do Rio Verde - UNINCOR. Three sets of each exercise were performed, with a recovery interval of 2 minutes between sets, and only after the three sets of the same exercise was the sequence for the next exercise performed. The participants were evaluated by ultrasonography to assess the thickness of the vastus lateralis muscle; strength evaluation test of the extensors and flexors of the knee by means of maximum voluntary isometric contraction evaluated by a traction dynamometer and maximum dynamic strength evaluated by means of one repetition maximum tests; and functional performance tests (Single/Triple Hop Test and Vertical Jump). The results showed that groups G40 (Δ=0.73cm) and G80 (Δ=0.56cm) showed similar gains in muscle thickness of the vastus lateralis. Both groups showed significant differences compared to the control group GC (Δ=-0.33cm; p=0.0001). For muscle strength gains, of the knee extensor muscles, assessed by means of a traction dynamometer (MVIC - Maximum Voluntary Isometric Contraction) strength gains were observed in intervention groups G40 (Δ=5.82kg) and G80(Δ=8.37kg). Both groups show significant differences in relation to the CG (-0.015kg; p=0.0001). No significant differences were observed in the knee flexors evaluation (p=0.1251). In the dynamic strength evaluation (1RM), G80 showed the greatest strength gains when compared to G40 and CG (p<0.0001). These differences were observed in the Leg Press exercises (Δ=65.42kg), extension chair (Δ=13.52kg) and flexor table (Δ=7.89kg). In the functional evaluation through the achieved distance significant differences were found between the groups, with the G80 group showing the greatest gains in distance when compared to G40 and GC in the Single Hop Test (p=0.0001), Triple Hop Test (p=0.0001) and Vertical Jump (p=0.0001). We can conclude that resistance training to concentric failure performed at high or low load intensities generates similar muscle hypertrophy gains. However, for the gain of dynamic maximal strength, voluntary isometric maximal strength and for the functional performance tests, high load intensities are more effective when compared to low load intensities. Study 2 aimed to evaluate the acute effects in a resistance training session to concentric failure with different load intensities (40% vs. 80% RM) on mineral metabolism (sodium, potassium, magnesium, calcium, phosphorus, zinc), indirect markers of stress and

muscle damage (creatine kinase, oxalacetic transaminase, infrared thermography, lactacidemia). An experimental study was conducted with physically active male subjects aged 18 to 25 years. Twenty-eight men met the inclusion requirements for the study, fourteen in each group. The first group performed the training protocol with a training load intensity of 40%RM (G40). The second group trained at 80%MR (G80). The training program with resisted exercises to concentric failure consisted of three sets of Leg Press, extension chair, and flexor table exercises, with a 2 minute interval between sets. According to the results there was a significant difference between the two groups for the concentration of sodium (p=0.026), potassium (p=0.0001), calcium (p=0.0021), lactate (p=0.011) and oxalacetic transaminase (p=0.011). We can conclude that resistance training to concentric failure with higher load intensity leads to higher metabolic stress and muscle damage when compared to training with lower load intensity. Study 3 aimed to evaluate the acute hemodynamic effects of resistance training to concentric failure at different load intensities (40% vs. 80%RM). An experimental study was conducted with physically active male subjects aged 18-25 years with experience in resistance training. Twenty-eight males met the inclusion requirements for the study, fourteen in each group. The first group performed the training with the load intensity at 40%RM (G40), while the second group at 80%RM (G80). The training session until concentric failure was performed in the knee extension exercise (extensor chair). Three sets of the exercise were performed with a 2 minute interval between sets. The participants were evaluated by the behavior of systolic blood pressure, diastolic blood pressure, heart rate, and the double output. The blood pressure and heart rate values were evaluated at the last repetitions of each exercise and after 5 and 15 minutes. The results showed that in none of the training situations evaluated there were significant interactions between the factors of systolic blood pressure (p=0.172), diastolic blood pressure (p=0.298) heart rate (p=0.376) and double product (p=0.214). The mean double product, an important cardiovascular risk parameter, showed maximum mean values of: G40=12363.6 mmHg x bpm and G80=11363.6 mmHg x bpm . Thus, we can state that resistance training to concentric failure with 40 and 80%RM are safe, because, according to the guidelines of the American College of Sports Medicine (2014), values up to double product equal to or above 30,000 mmHg x bpm (millimeters of mercury/beats per minute) are indicative of cardiovascular risk