Lets talk about the anatomy of the hamstring muscles group. The hamstrings consists of three main muscles which are located posteriorly at the back of your thighs as shown in the diagrams below.
The main function of the hamstring muscles is to flex the knee joint as well as extend the hip joint, they also either laterally or medially rotate the knee joint. The Biceps Femoris muscle (most commonly injured) originates from ischial tuberosity (long head) and lateral lip of linea aspera (short head) and inserts to the head of the fibula. Semimembranosus muscle (deeper muscle) originates from ischial tuberosity and inserts to the posterior aspect of medial condyle of tibia. Semitendinosus also originates from ischial tuberosity and inserts to the proximal, medial shaft of the tibia at pes anserinus tendon.
The primary football association audit of injuries study in soccer reported that 12% of all injuries in male soccer players throughout two seasons were indicated to be as hamstring strains. This shows that players were 2.5 times more likely to suffer from a hamstring strain than a quadriceps strain during a match. According to research, 23-28% of all injuries have been classified as thigh injuries (hamstrings); with bicep femoris accounting for 81% of all hamstring injuries. In one season of soccer, a total of 41,474 training days are missed due to hamstring strain injuries; an average of 21.5 days missed per injury.
Numerous predisposing aetiological factors have been suggested to have an influence on hamstring strain injuries risk including insufficient warm-up, previous injury, eccentric hamstring weakness and ipsilateral muscle strength imbalance between hamstrings and quadriceps.
The sequential pattern of match play correspondingly shows fatigue to be a risk factor in injury mechanism, as players tend to fatigue in the latter stages of each half in soccer game. This showed 5-10% decrease in total distance covered in the second half of a soccer match. As a result of fatigue occurring in the muscles, the force within the muscles decreases resulting in reduction of the energy absorption capabilities, which increases the possibility for injury to occur.
Biomechanical studies stated that during the high-speed running phase which constantly occurs late in the swing phase of the gait cycle, the hamstrings are activated throughout the complete cycle with peaks in activation during the terminal swing and early stance phases. During deceleration the hamstrings are eccentrically contracting in a lengthened position reaching their maximum length under force.
High-speed running constantly occurs late in the swing phase of the gait cycle, simultaneously; hamstrings work eccentrically to decelerate the lower limb from an acceleration in preparation for ground contact as shown in the diagram below. Therefore, the acceleration phase will increase the running velocity and the forces in the knee extensors, as the results of knee flexors being weaker and fatigued, the muscles will be accepting larger forces causing overload on the mechanical limits of the tissue. Bicep Femoris, the long head (attached to the ischium) undergoes the highest stretch, reaching greater length of 110% upright standing during terminal swing.
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