# Measurement of the Impact Loads to Reduce Injuries in
## 1 Introduction  
Acrobatic gymnastics is a sport that includes physical exercises requiring balance, strength, flexibility, agility, coordination, and endurance, having started in the 17 th century with the creation of the circus [1]. Acrobatic gymnastics is performed to the sound of music and on a 12 \(\times\) 12 m practicable In official competitions, acrobatic gymnastics offers five different possibilities for partnerships: male, female, and mixed pairs; women's groups (three gymnasts), and men's groups (four gymnasts) [2]. Due to the high number of jumps, there is constant and repetitive landing contact with the practicable, sometimes made from a significant height, and, consequently, the possibility of gymnasts suffering injuries [3], especially in the lower limbs, is considerable [4; 5; 6]. Assessing the loads involved during landings is very important to improve the athlete's performance, help coaches develop landing techniques, and, consequently, reduce injuries [7]. During the landing phase, due to the impact on the surface, differences were observed in the knee and quartile that are directly linked to the reaction force [8]. According to [PERSON] et al. [9], the high-impact forces that arise in athletes' lower limbs during gymnastics landings contribute to the high injury rate. However, it is not just injuries to the lower limbs that can occur during landings; injuries to the lumbar spine of gymnasts are also very common, due to the rotation of the spine during the flexion and extension of the lower limbs [10]. [PERSON] et al. [11] conducted a study to determine the effect of impact on the average rate of loading during a forward hop jump. The vertical load of impact during the jump was characterized using the peak load, time to peak, and impulse. The performance of gymnasts is related to their jumping ability, the form of landing, and their jumping routines [12]. The high number of jumps they perform, which involves repeated stretching-shortening cycles of the muscles, can produce muscle fatigue of the lower limbs and lead to injuries [13; 14; 15]. According to [PERSON] et al. [16], the vertical jump can provide important information that can be used to analyze the muscular fatigue that happens during vertical jumps in acrobatic gymnastics. The ankle power and the ground reaction load reduce with fatigue, due to the fact that fatigue affects ankle biomechanics by reducing dorsiflexion, from initial contact to maximum knee flexion at landing, and power during the jump [17]. The main injuries in gymnasts occur in the lower extremities (42.3%), namely in knees (16.6%) and heels (12.9%) [18; 19; 20]. Therefore, understanding how the gymnasts perform landing is important for injury prevention. The identification of training routines and landing movement patterns that may be a risk factor for injury can help advise on how to change landing movements or training routines in order to prevent or eliminate the possibility of injury [21]. The high vertical impact loads on the lower limbs during landing, due to repetitive exposure, are one of the main injury factors. This probability of injury occurring can be reduced if gymnasts are instructed and trained in landing techniques [22; 23]. According to [PERSON] et al. [24], to avoid injuries during landing, it is necessary to define the landing strategy considering the vertical reaction of the ground loads and shorter braking phase during the landing. In addition, jump heights have a great influence on landing forces, especially the ones developed by the muscles of the lower limbs. To reduce the possibility of injury, gymnasts are usually trained to land with stiff lower limbs, shortening the braking phase [22; 25]. According to [PERSON] et al. [26], landing is a crucial factor in gymnastics competitions because it is a complex movement under neuromuscular control, involving space-time prediction of the moment of contact with the ground, as well as the magnitude of the vertical ground reaction force being dependent on the gymnast's body weight.