Your hamstrings factor heavily into the motion used to propel yourself while running. The physiology of taking a stride and swinging the leg through for another stride combined with the impact of each foot strike places tremendous strain on all the muscles of the legs. Due to the physical demands of the activity, running is not recommended with a pulled hamstring until you reach a full recovery from the injury.
Extent of Injury
The American Academy of Orthopaedic Surgeons says a hamstring pull or strain occurs when the major muscle in the back of the thigh is torn or stretched. A mild strain may be no more than a slight pull causing stiffness, but a more severe strain can mean tearing of the muscle or possible complete rupture of the tissue.
Hamstrings and Running
A study by Elizabeth Chumanov appearing in the March 2011 issue of "Medicine & Science in Sports & Exercise" explains that the hamstrings are most active in the swing phase of the gait cycle as your leg leaves the ground and strides forward for the next step. The study also concludes that increased speed also increases the stress load on the hamstring. Based on this information, there is little or no way to avoid engaging the hamstrings while running. Therefore, running with a pulled hamstring may only exacerbate the existing injury and push it to tear or rupture.
Treatment and Recovery
Medline Plus explains that the extent of recovery time depends on the severity of the pull. A mild pull can result in pain and stiffness for a few days. A more severe pull can cause pain for up to two weeks. The first step to recovery is rest which requires you cease any activity that strains the injure muscle further including running. Mild strains can recover with rest, ice, compression, elevation and over-the-counter anti-inflammatory medication. When experiencing a hamstring pull, be sure to consult your health care professional for an accurate diagnosis and plan for recovery.