THE SPORTING HAMSTRING: PART 1
Hamstring injuries are common in sports that involve high-intensity sprinting efforts, such as the various forms of football and track and field. They are also prevalent in dance/ballet/hurdles due to the combination of explosive movements and flexibility. These athletes tend to suffer ‘overstretch’ type injuries and often to the proximal hamstring (closer to the hip), whereas the typical sprinter tends to suffer a contractile injury during the eccentric phase of running (muscle activating whilst lengthening). Recent studies from the professional level show that hamstring strains alone rank as the first or second most common injury in soccer, Australian Rules football, rugby and American football. Acute hamstring injuries also have a high recurrence rate, approaching 30% (within the same season) in Australian Rules football.
The hamstrings muscle group is composed of three muscles:
- Biceps femoris (short head and long head)
All of them (except the short head of the biceps femoris) have their origin at ischial tuberosity on the pelvis and they insert at the inside and outside of the lower leg right below the knee. This means that they overlap two joints – they extend the hip joint and flex (bend) the knee joint.
PROPOSED MECHANISM OF INJURY
Gait analyses during running demonstrates that the hamstrings undergo an eccentric (muscle lengthening) contraction during the last 25% of the swing phase (just before your foot hits the ground), and this is when most injuries occur…but WHY?
- High Forces: the hamstrings must work to oppose both the high hip flexion and knee extension forces for a controlled foot strike
- Length Tension Relationship: the ability of muscle fibres to contract and create tension to withstand forces varies dependant on its length. This may be compromised in the late swing phase in which the hamstrings are being lengthened across both hip and knee joints.
These observations are helpful when designing rehabilitation programs or putting in place preventative measures. There are however a large number of contributing factors that may predispose individuals to such injuries, and need to be addressed in addition to conventional strengthening. Hamstring injuries are in fact quite complex, with each individual’s loading mechanics and injury profile extremely variable.
Previous hamstring injury
Formation of scar tissue
Ongoing neuromuscular deficits
Ongoing functional compensations
Reduced hip ROM
Hip flexors/quadriceps length
Hamstrings to quadriceps strength ratio
Eccentric hamstring strength
Eccentric hamstring strength asymmetry
Muscle fibres type 1 vs 2
Core control and lumbar spine pathology
|Level of play
Increases or changes in the training programme (particularly intense periods of training)
Hamstring injuries continue to trouble sporting individuals and clubs despite a growing body of research. What we know is hamstring injuries are far more complex than simply an ‘overstretched’ muscle. The hamstring muscles are highly sensitive to load changes throughout the kinetic chain and every individual’s body transmits load differently. It is crucial that individuals work with their physiotherapists to establish a rehabilitation program that address each risk factor specific to them and their sport.