Athelts that meet the inclusion criteria will be randomized into two groups. The experimental group will receive an 8-week (3 days per week) specificl protocol based on hamstring strengthening (isometric, concentric and excentric exercises), and the control group will not receive any additional exercise. The aim of the study is to investigate the changes in hip and knee muscle strength, in the extensibility of cuadriceps, hamstrings and hip abductors, in the physical functions and in the final marks.

Inclusion Criteria:

• Professional Athlet
• 3 or more trainign days
• Previous hamstring injury but without symptoms for 3 months or >30% difference between cuadriceps and hamstrings strength (considered as a risk for hamstring injury)

Exclusion Criteria:

• Sistemic pathologies
• Any other type of musculoskeletal injuries in lower limb or lumbar spine
• To have a previous specific protocol
• To skip more than 3 training days
• General contraindications for physical activity

Single-blind