The relationship between force and the velocity at which a load can be moved is known as force-velocity (F-V) curve. Methods that control strength training intensity based on F-V curves have been proposed. However, F-V curves available were built for a specific European population. Moreover, those curves need to be revisited since they ignored one factor that strongly affect their kinetics, namely muscle fibre type composition. We propose that F-V curves must consider the functional and metabolic profile of the athletes, and hypothesise that at least two F-V curves with different kinetics can be built. Then, we evaluated whether there are differences in speed during the concentric phase of the deep squat at submaximal loads and also built F-V curves according to the different functional and metabolic profile of the athletes.
An analytical, cross-sectional observational study involving 147 elite team sports athletes (basketball, handball, softball, indoor soccer, field soccer, volleyball floor and beach volleyball) was carried out in Medellín, Colombia. All athletes (19.3 ± 3.2 years old, 51.7% men) underwent a medical and anthropometric evaluation, as well as six physical tests: free vertical, counter movement, and squat jumps, 20 metres and fly 20 metres sprint tests and ergospirometry. A cluster analysis that included the results of physical tests allowed us to classify athletes as “powerful” or “endurance”. The speed at submaximal loads (30%, 40%, 50%, 60%, 70% and 80% of maximal load lifted), measured with an isoinertial force transducer during the concentric phase of the deep squat, allowed us to build F-V curves. Moreover, a subsample of 49 athletes (38.8% men) was evaluated by proton resonance magnetic spectroscopy for noninvasive quantification of intramuscular carnosine in their vastus lateralis muscle (VLM), in order to estimate the area occupied by type II fibres.
66 athletes were classified as powerful and were different in body composition and physical tests results compared to endurance athletes (p < 0.01). A multivariate model adjusted for age, sex, body mass index (BMI) and body fat percentage, showed significantly higher values in powerful vs. endurance athletes in maximal load (15.6%), velocities at all submaximal loads (5.6%), load values (15.9%), and maximal power (20.5%), giving F-V curves with different kinetics between both groups of athletes. After adjusting for age, BMI and body fat percentage, the carnosine concentration in VLM was higher in powerful athletes (4.5 ± 0.2 mM/Kg.wt, n = 26) than in endurance ones (3.6 ± 0.2 mM/Kg.wt, n = 23; P < 0.01). This corresponded to a higher (P < 0.01) area occupied by fibres type II in powerful (38.2 ± 1.6%) than endurance (29.5 ± 1.4%) athletes.
In conclusion, there are differences in speed during the concentric phase of the deep squat at submaximal loads according to the functional profile of the athletes. This establishes two F-V curves with different kinetics, which consider the fact that powerful athletes have more area of type II fibres in their VLM. These are the first F-V curves built for different types of team sports athletes taking into account their muscle fibre type composition and reconcile sports medicine tests with knowledge obtained from basic sciences studies on skeletal muscle