- Aug 16, 2003
- 8,274
- 12,242
http://www.aspetar.com/journal/viewarticle.aspx?id=88#.VqkACfnhDIU
PREVENTING HAMSTRINGS STRAINS: A CURRENT VIEW OF THE LITERATURE
– Written by Roald Bahr, Qatar and Norway
Muscle injuries occur frequently as contusion injuries in contact sports and as strains in sports involving maximal sprints and acceleration. Among sprinters, hamstring strains represent approximately 1/3 of all acute injuries1. Since the different football codes (soccer, rugby, American football, Australian Rules football) combine maximal sprints with frequent player-to-player contact, it is not surprising that a sizable proportion of injuries are thigh injuries. In fact, recent studies from the professional level show that hamstring strains alone rank as the first or second most common injury in soccer2-5, Australian Rules football6,7, rugby8,9 and American football10,11, in most studies accounting for one in every five to six injuries. There also appears to be a trend with a gradual increase in the proportion of hamstring strains compared to other injury types such as ankle sprains when compared to data from studies from the 1980s12. However, it should be noted that quadriceps strains are also common in soccer4 and that muscle contusion injuries to the quadriceps muscles account for a significant proportion of all football injuries at the elite level. Hamstring strain injuries are also common in sports where the muscles may be stretched past the usual range of movement (ROM) e.g. dancing and water-skiing13.
INJURY MECHANISMS
There are two main mechanisms involved in thigh muscle injuries:
The contusion mechanism is straightforward. The player is typically injured by a direct blow from an opponent, usually the knee hitting the lateral thigh in a tackle (a.k.a. ‘charley horse’ or ‘cork thigh’). The muscle is thereby crushed between the opponent’s kneecap and his own femur.
The injury mechanism for hamstring strains are less well understood. The hamstrings muscle group is composed of three muscles:
All of them (except the short head of the biceps) have their origin at ischial tubercle 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 straighten the hip joint and bend the knee joint. Muscle strains usually occur in the interface between the muscle and its tendon (the myotendinous junction), but avulsion injuries from the ischial tubercle are also seen.
Hamstring strains most often occur during maximal sprints. It is difficult to document exactly at what time during the running cycle injuries occur14. However, since the net moment developed by the hamstrings is thought to be maximal in the late swing phase, right before heel strike, this is thought to be a vulnerable position15,16. In this instance, the hamstring muscles work eccentrically. Another suggestion is at push-off. Strain injuries to the quadriceps muscles have been less studied, but are thought to mainly result from kicking the ball.
RISK FACTORS
A number of candidate risk factors have been proposed for hamstring strains, the most prominent being the following four internal factors (see Text Box 1):
In theory, limited ROM for hip flexion could mean that muscle tension is at its maximum when the muscle is vulnerable close to maximum length. However, this hypothesis has yet to be confirmed, since there are several studies on soccer players suggesting that hamstring flexibility is not a risk factor for strains18,19. However, other studies from soccer and Australian Rules football have shown low quadriceps flexibility to represent a risk factor for not only hamstrings20, but also quadriceps strains21.
Low hamstring strength would mean that the forces necessary to resist knee extension and start hip extension during maximal sprints could surpass the tolerance of the muscle-tendon unit. Hamstring strength is often expressed relative to quadriceps strength as the ‘hamstrings: quadriceps ratio’, since it is the relationship between the ability of the quadriceps to generate speed and the capacity of the hamstrings to resist the resulting forces that is believed to be critical. Several studies show that players with low hamstring strength or ‘low hamstrings: quadriceps strength’ ratio or ‘side-to-side strength imbalances’ may be at increased risk of injury17.
A history of previous hamstring strains greatly increases injury risk, as documented in numerous studies17,22,23. Injury can cause scar tissue to form in the musculature, resulting in a less compliant area with increased risk of injury. A previous injury can also lead to reduced ROM or reduced strength, thereby indirectly affecting injury risk. Football players with a history of previous hamstring injury have a seven times higher risk of injury than healthy players and as many as 13% can expect to suffer a new injury during one season.
Older players are at increased risk for hamstring strains. Although older players will be more likely to have a previous injury, increased age is also a risk factor independent of a history of previous injury19,23.
Other risk factors, which have been suggested but are less well-studied, include:
Players of black or aboriginal origin sustain significantly more hamstring strains than white players23. It has been suggested that these players may be faster runners compared to their white counterparts, possibly because of a higher proportion of type II muscle fibres. A faster running speed will generate higher hamstring torques, which may explain the increased injury risk.
PREVENTING HAMSTRINGS STRAINS: A CURRENT VIEW OF THE LITERATURE
– Written by Roald Bahr, Qatar and Norway
Muscle injuries occur frequently as contusion injuries in contact sports and as strains in sports involving maximal sprints and acceleration. Among sprinters, hamstring strains represent approximately 1/3 of all acute injuries1. Since the different football codes (soccer, rugby, American football, Australian Rules football) combine maximal sprints with frequent player-to-player contact, it is not surprising that a sizable proportion of injuries are thigh injuries. In fact, recent studies from the professional level show that hamstring strains alone rank as the first or second most common injury in soccer2-5, Australian Rules football6,7, rugby8,9 and American football10,11, in most studies accounting for one in every five to six injuries. There also appears to be a trend with a gradual increase in the proportion of hamstring strains compared to other injury types such as ankle sprains when compared to data from studies from the 1980s12. However, it should be noted that quadriceps strains are also common in soccer4 and that muscle contusion injuries to the quadriceps muscles account for a significant proportion of all football injuries at the elite level. Hamstring strain injuries are also common in sports where the muscles may be stretched past the usual range of movement (ROM) e.g. dancing and water-skiing13.
INJURY MECHANISMS
There are two main mechanisms involved in thigh muscle injuries:
- Direct (contusion) injuries.
- Indirect (distension or strain) injuries.
The contusion mechanism is straightforward. The player is typically injured by a direct blow from an opponent, usually the knee hitting the lateral thigh in a tackle (a.k.a. ‘charley horse’ or ‘cork thigh’). The muscle is thereby crushed between the opponent’s kneecap and his own femur.
The injury mechanism for hamstring strains are less well understood. The hamstrings muscle group is composed of three muscles:
- Semimembranosus
- Semitendinosus
- Biceps femoris.
All of them (except the short head of the biceps) have their origin at ischial tubercle 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 straighten the hip joint and bend the knee joint. Muscle strains usually occur in the interface between the muscle and its tendon (the myotendinous junction), but avulsion injuries from the ischial tubercle are also seen.
Hamstring strains most often occur during maximal sprints. It is difficult to document exactly at what time during the running cycle injuries occur14. However, since the net moment developed by the hamstrings is thought to be maximal in the late swing phase, right before heel strike, this is thought to be a vulnerable position15,16. In this instance, the hamstring muscles work eccentrically. Another suggestion is at push-off. Strain injuries to the quadriceps muscles have been less studied, but are thought to mainly result from kicking the ball.
RISK FACTORS
A number of candidate risk factors have been proposed for hamstring strains, the most prominent being the following four internal factors (see Text Box 1):
- age,
- previous injury,
- reduced hip ROM and
- poor hamstrings strength17.
In theory, limited ROM for hip flexion could mean that muscle tension is at its maximum when the muscle is vulnerable close to maximum length. However, this hypothesis has yet to be confirmed, since there are several studies on soccer players suggesting that hamstring flexibility is not a risk factor for strains18,19. However, other studies from soccer and Australian Rules football have shown low quadriceps flexibility to represent a risk factor for not only hamstrings20, but also quadriceps strains21.
Low hamstring strength would mean that the forces necessary to resist knee extension and start hip extension during maximal sprints could surpass the tolerance of the muscle-tendon unit. Hamstring strength is often expressed relative to quadriceps strength as the ‘hamstrings: quadriceps ratio’, since it is the relationship between the ability of the quadriceps to generate speed and the capacity of the hamstrings to resist the resulting forces that is believed to be critical. Several studies show that players with low hamstring strength or ‘low hamstrings: quadriceps strength’ ratio or ‘side-to-side strength imbalances’ may be at increased risk of injury17.
A history of previous hamstring strains greatly increases injury risk, as documented in numerous studies17,22,23. Injury can cause scar tissue to form in the musculature, resulting in a less compliant area with increased risk of injury. A previous injury can also lead to reduced ROM or reduced strength, thereby indirectly affecting injury risk. Football players with a history of previous hamstring injury have a seven times higher risk of injury than healthy players and as many as 13% can expect to suffer a new injury during one season.
Older players are at increased risk for hamstring strains. Although older players will be more likely to have a previous injury, increased age is also a risk factor independent of a history of previous injury19,23.
Other risk factors, which have been suggested but are less well-studied, include:
- race,
- gender,
- level of play,
- player position,
- improper running technique,
- superior running speed (peak performance),
- low back pain,
- increases or changes in the training programme (particularly intense periods of training),
- insufficient warm-up and
- muscle fatigue.
Players of black or aboriginal origin sustain significantly more hamstring strains than white players23. It has been suggested that these players may be faster runners compared to their white counterparts, possibly because of a higher proportion of type II muscle fibres. A faster running speed will generate higher hamstring torques, which may explain the increased injury risk.