A meta-analysis article showed evidence that a history of hamstring injury and being of older age were associated with increased risk of hamstring strains. One study found that men and master athletes (athletes older than forty) were at an increased risk of hamstring strains compared with women and younger athletes. Women were approximately 3 times more likely to develop hamstring strain than males with the majority of these being non-sporting scenarios. Similarly the average age of non-sporting hamstring strains are from the ages of 40–60. Many of these non-sporting injuries are sustained during road traffic accidents, slipping, and falling. These results also show that hamstring strains account for 50% of muscle injuries received by sprinters and are the most common injury in hurdling. One explanation is that older active individuals may be at greater risk due to lower levels of eccentric knee flexor strength compared with their younger counterparts. However, it is unclear whether flexibility serves as a risk factor; this topic should be researched in the future to further understand the relationship between flexibility and risk of injury. Muscle weakness has also been an implication as a predisposing factor for both primary and recurring hamstring strain injuries. Over a 10-year study more than 51.3% of hamstring strains occurred during the preseason of athletics. In another study, that analyzed 25 NCAA sports over four years, it was clearly shown that hamstring strain rates are higher in the preseason.
Straining of the hamstring, also known as a pulled hamstring, is defined as an excessive stretch or tear of muscle fibers and related tissues. Hamstring injuries are common in athletes participating in many sports. Track and field athletes are particularly at risk, as hamstring injuries have been estimated to make up 29% of all injuries in sprinters. Hamstring injuries can also come with a hip injury from sprinting. Symptoms for a hip injury are pain, aching and discomfort while running or any physical exercise. The biceps femoris long head is at the most risk for injury, possibly due to its reduced moment of knee and hip flexion as compared to the medial hamstrings. Causes of hamstring strain
The muscle group is prone to injuries due to the explosive nature of movement in sports and thus causing overload and overstretching of the hamstring musculature. The other causes may be:

Previous injury
Poor muscle strength
Poor flexibility
Inadequate warm-up
Fatigue
Imbalance
OveruseThis condition is most commonly seen in:

Athletes involved in soccer, baseball, football, rugby
Dancers and water skiers
Sports involving cross-country skiing, downhill skiing, judo, cricket, and bull riding

Diagnosis
Grades
Grade 1
Sensation of cramp or tightness and a slight feeling of pain when the muscles are stretched or contracted. Grade 2
With a grade two hamstring strain there is immediate pain which is more severe than the pain of a grade one injury. It is confirmed by pain on stretch, swelling and contraction of the muscle. Grade 3
A grade three hamstring strain is a severe injury.