Strength training is widely known as an effective way to promote muscle growth. This morphological adaptation is essential for improved athletic performance and provides numerous health benefits, including prevention of metabolic diseases. However, the mechanisms responsible for the similar muscle growth achieved by training with heavy and light loads have not yet been fully elucidated. study(1) A recent study published by Renato Barroso and colleagues in the journal Metabolites attempts to fill this gap.
The study in question examined general metabolic responses and electromyography (sEMG) signal amplitude to heavy load (HL) and light load (LL) training. The researchers measured muscle thickness via ultrasound, sEMG signal amplitude via electromyography, and analyzed metabolites expressed via metabolism.
The study used 30 healthy young men who had not weight trained for at least 12 months before the study. Participants were randomly divided into two groups: high load (HL) and low load (LL). They underwent an eight-week training programme, during which blood samples were taken for subsequent metabolic analysis during the first and last training sessions.
- Participants : Thirty healthy young men, who had not participated in resistance training programs for at least 12 months before the study, were recruited for the experiments. Individuals with metabolic diseases, such as diabetes, who followed a low-calorie diet, or who had osteoarticular problems that could interfere with exercise performance were excluded from the study.
- Experimental design : Participants completed two familiarization sessions with the 1-RM test in the 45° leg press and bilateral leg extension exercises. After familiarization sessions, a test-retest 1-RM of the exercises was performed. There was at least 72 hours between laboratory visits.
- Maximum dynamic force : Maximum dynamic strength was determined using the 1 repetition maximum (1RM) test according to the American Society of Physiologists (ASEP) guidelines for leg press and leg extension exercises.
- Training protocol : Participants performed two training sessions per week using the 45-degree leg press and bilateral leg extension, in that order, for eight weeks.
- Muscle activation : Muscle activation was assessed by surface electromyography (EMG) obtained only in the 45° leg press exercise using a 16-channel EMG.
- Muscle thickness : B-mode ultrasound was used to capture images of the thickness of the rectus femoris, vastus intermedius, and vastus lateralis muscles.
- Blood sample : The blood sample was taken after the participants arrived at the laboratory after fasting for 10 hours, eating a standard meal, and resting for one hour.
- Sample preparation for metabolic analysis : Before analysis, the 3 kDa filter was washed. After washing, 350 μl of stored serum was added to the filter, which was centrifuged at 14,000 rpm for 45 min at 4°C.
- NMR data acquisition and quantification : To obtain the spectra, 1H-NMR spectroscopy at 600 MHz was used. The analysis was performed at a constant temperature of 298 K (25 °C). A total of 256 scans were performed, with a delay interval of 1.5 s and an acquisition time of 4 s between each scan.
- statistical analysis : Data were presented as mean and standard deviation. The distribution of data was verified by the Shapiro-Wilk test. For comparisons between and within groups, linear mixed models for repeated measures were used, assuming participants were a random factor, and group (HL and LL) and time period (pre- and post-training) as fixed factors for muscle thickness variables. , EMG amplitude, and macronutrient consumption.
- Metabolic response : After the experimental sessions of the HL and LL groups and the performance of 1H-NMR spectroscopy, 50 metabolites were identified and quantified in the blood serum of the two groups. Principal component analysis (PCA) was performed to determine overall metabolic response patterns by the HL and LL groups.
The study found that the HL and LL groups showed no symptoms There were no significant differences in metabolic response and muscle thickness. However, increased sEMG amplitude was observed in the HL group. Interestingly, a relationship was observed between changes in muscle thickness in the vastus lateralis muscle in the HL group and the levels of some metabolites (carnitine, creatine, 3-hydroxyisovalerate, phenylalanine, asparagine, creatine phosphate, and methionine); While in the LL group, a relationship was observed between changes in muscle thickness of the vastus lateralis muscle and the levels of some other metabolites (acetoacetate, creatine phosphate and oxypurinol).
Analysis and interpretation
The study authors suggest that the mechanisms responsible for the similar muscle growth achieved with these two different types of training may be related to the characteristics of the activated muscle fibers, metabolic demand, and the process of protein synthesis.
For bodybuilders, these results suggest that in terms of muscle hypertrophy, eating heavy loads is not necessary and that working with light loads can be just as effective in stimulating muscle growth. This confirms the results of this study, in which the authors concluded that muscle gain is similar regardless of load, as long as the sets are failed. However, as another study with the same conclusion points out: “Light weight training can be used to stimulate muscle growth just as effectively as heavy weight training. However, fatigue may persist longer after training with light loads, which may limit training frequency and weekly training volume.” in the end.
Should you take heavy or light loads?