This study investigates muscle agenesis, specifically the absence of the palmaris longus and plantaris muscles, and its effects on injury risk, strength, and performance. Muscle injuries are common in sports, and the presence or absence of certain muscles can impact biomechanics and injury susceptibility. The study involves 132 subjects, divided into those with and without muscle agenesis, assessing injuries with the Nordic and CMDQ questionnaires and measuring strength with dynamometers. Results aim to clarify the controversial impact of muscle agenesis on functional disability and performance adaptation in the scientific literature.

Background. This study examines muscle agenesis, a congenital condition that involves the absence of a muscle, focusing on the palmaris longus and plantaris muscles. The prevalence of palmaris longus agenesis varies significantly, and there is debate about whether its absence results in functional disability or is a predictor of injuries. Muscle injuries account for one-third of sports injuries and more than 30% of all musculoskeletal system injuries. The presence or absence of certain muscles can influence the body's biomechanics and, therefore, susceptibility to injuries, as muscles play a crucial role in generating force and coordination, hence movement. The absence of certain muscles may require other muscles to compensate, which could affect the efficiency and performance capacity in certain body areas. However, in many cases, the absence of a muscle may not have a significant effect on performance, as other muscles can adapt to perform its function. This study seeks to provide clarity in this area of research due to the existing controversy in the scientific literature.

Objectives. To determine if muscle agenesis influences the development of injuries and its impact on strength and performance.

Material and methods. An observational analytical cross-sectional study was conducted with 132 subjects divided into one group of 66 subjects with muscle agenesis and another group of 66 subjects without muscle agenesis. The primary variable is the presence of upper and lower limb injuries measured using the Nordic and CMDQ questionnaires, and the secondary variable is upper limb strength measured with a dynamometer in palmar flexion and hand grip tests; and lower limb strength measured with a dynamometer in plantar flexion and vertical jump tests. The measurements were taken over 1 hour and 30 minutes during two days, with a 48-hour interval between the measurements of the upper and lower limbs.

Inclusion Criteria:

• Individuals who lead a sedentary lifestyle or who are not used to doing physical training on a regular basis (more than 2 h/week).
• People between 18 and 80 years old.

Exclusion Criteria:

• Individuals with an ongoing oncological process.
• People with an active infectious process.
• Subjects with psychiatric disorders.
• Individuals with intellectual disorders that prevent understanding of the intervention.
• People with judicial incapacity.
• Patients diagnosed with fibromyalgia.
• Pregnancy or probability of pregnancy.
• Individuals with sensory impairments in the hand that prevent manual pressure.

People with and without muscle agenesis.