The body has hundreds of muscles of various types—slow twitch, fast twitch, skeletal, smooth and cardiac, to name a few. Muscles provide their power by contracting and relaxing, thereby generating a force that causes movement. Running muscles require a strong anchor (where one end of the muscle attaches to a bone or ligament) and the other end of the muscle connects to the flexible part of the limb. When that muscle contracts or shortens, movement of the joint is produced.
The science behind this muscle contraction and relaxation is very complex. It involves proteins called actin and myosin, along with various other elements including calcium, potassium, sodium and water. This is why it is so important to supply the fuel (water, electrolytes, etc.) for the muscles to work while you are training.
When muscles contract harder and faster, movement is produced and running speed increases. This is called concentric contraction: the muscle is shortening and tightening, thus generating movement. However, not all muscle contractions are associated with the generation of movement. For instance, when you run down a hill, some muscles are contracting to generate movement. At the same time, though, the elongated muscles are also contracting to decelerate your legs and prevent you from losing control. This is called eccentric contraction. In long distance runners, muscle injuries have been shown to occur more frequently in the eccentric phase than in the concentric phase. Sprinters, on the other hand, may be more prone to suffer injuries from a sudden muscle contraction as seen in the concentric phase.
Your muscles are prone to being injured through the usual mechanisms: fatigue, training errors, improper shoe wear, running on dangerous terrain, or anatomical factors such as weak or stiff muscles. A “strain” refers to a muscle injury whereas a “sprain” usually means a ligament injury. Muscles are injured when they sustain small tears in their fibres, and these “micro tears” cause a small hemorrhage (bleeding) in the muscle belly. This is usually self limited and doesn’t last long. Any extra fluid added to a muscle belly is painful, as seen after an immunization or intramuscular antibiotic injection. The repair process, or inflammation, then takes over to heal the injury—this also prolongs the pain until healing is complete.
Muscles that are more prone to strains are the ones that control the movement of two adjacent joints, such as the psoas (flexing both the spine and the hip) or the rectus femoris (quadriceps) which bends or flexes the hip while simultaneously straightening or extending the knee. If the body can’t fully stabilize one of the two joints, the muscle will contract or tighten without the necessary anchor, which can results in a tear of the muscle fibres. An actual muscle strain (stretch or tear) can be felt following a sudden forceful tightening of the muscle as seen in a quick sprint. It can also follow a more slowly elongated pull of the muscle from running downhill. Following a muscle pull, you may actually feel the muscle as a tight “knot” that can be very tender to the touch. It will become sore to run as you stretch out the muscle, and it may cause you to limp.
The location of the pain in a muscle will help identify which muscle has been injured. A strain of the hip adductor muscle, for instance, will be felt along the upper inside of the thigh. A quadriceps muscle strain will be felt over the front surface of the thigh. The calf muscle or gastrocnemius (and possibly its partner, the soleus muscle) will give you pain in the back of your calf if it is strained. Hamstring injuries (often due to over-striding) will cause pain in the back of the thigh and lower buttock.
The initial management of these injuries doesn’t differ according to their location. The affected muscle should be rested and any strenuous movement of that muscle minimized. This means that when you suffer an acute strain, you should walk rather than run. Gentle stretches of the muscles, as one should be doing regularly, can be resumed early to prevent tightening of the injured muscle; however, the stretches should not be vigorous enough to cause pain in the area, as more damage to the muscle can occur.
Applying ice to the area is probably the most important early therapy. Place an ice pack, covered with a towel, over the area for 20 minutes, four times a day. Some runners obtain further relief by applying a compressive tensor bandage, which can be removed and rewrapped every few hours. During this acute phase, the use of over-the-counter pain medications can also be helpful.
The healing phase of a muscle strain begins very soon after the injury. Once the pain and swelling diminish—usually after two or three days for a mild strain—you can gently increase the intensity of the stretches and gradually advance toward your full activity level. Generally, let pain be your guide.
For more severe strains, however, a longer recovery time will be required. Self-treatment lasting for more than one week should not be continued if no improvement is occurring. At this stage, you should seek a medical practitioner who can confirm the diagnosis of a muscle strain and hopefully begin a more professionally and scientifically based treatment plan. The rehabilitation efforts will be directed at both the muscle strain itself and possibly at some underlying muscle weakness or imbalance that may have contributed to the problem.
Physiotherapists, massage therapists, chiropractors and trainers with a solid knowledge of the musculoskeletal system are able to assist in your recovery following a muscle strain. They can guide you on a personalized program which may involve a specific stretching regime for contracted or tight muscles. Some areas of weakness may have to be addressed through
Dr. Richard Beauchamp is an orthopedic surgeon based in Vancouver. He is the medical director of the Shriner’s Gait Lab at Sunny Hill Health Centre and a clinical professor in the Department of Orthopedics at the University of British Columbia. He is an avid runner and walker who has completed seven marathons.