The instant I leapt to catch a high-flying Frisbee, I felt a rip high inside the back of my leg, like a bungee cord fraying but not quite snapping. Before I hit the ground I knew I'd shredded a hamstring. I could still put weight on the wounded leg so -- idiotically, I know -- I tried to keep playing. My leg responded with an unequivocal, "No way, Jack!"

The hamstrings are a group of muscles running down the back of the thigh, between the "sitting bones" (ischial tuberosity to you) and the back of the knee. They work in concert with the quadriceps: When you bend your leg, the hamstrings contract and the quadriceps relaxes; the opposite happens when you extend. Or, in my case, the hamstring goes "boing!" and the quad wonders why its partner just bailed out.

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Hamstring strains threaten recreational walkers, pro athletes and anyone in between whose activities require either repeated extension and contraction of the muscle (walking, jogging) or explosive bursts (basketball, tennis, soccer, etc.).

Muscle strains are more likely in parts of the body where one muscle group is considerably stronger than its opposing number -- in this case, the powerful quad vs. the relatively meager hamstrings. The lesser muscles tire more quickly than the stronger ones and fail to respond to the demands of activity, causing the strain. This is precisely why we always lecture you on strengthening and stretching the muscles in the back of the body, and why I should really start attending those lectures.

Orthopedists classify hamstring injuries as Grade 1 (mild, some pain, maybe a limp), Grade 2 (noticeable pain, pronounced limp) or Grade 3 (severe, often leaves victim unable to stand or walk, with heavy bruising on back of thigh).

Most Grade 1 strains will heal with seven to 10 days of rest, coupled with gradually progressive strengthening exercises (needed to condition the new muscle fibers that the body lays down to repair the injury).

Grade 2 strains -- what I have -- require two to four weeks of similar treatment, often including physical therapy. Grade 3 tears can require surgery -- for example, if the hammy literally ripped in two -- and can take up to four months to fully heal.

My hamstring (or my rectus femorus, as I like to call it) tore near the place where the muscle morphs into tendon, close to the sitting bone. Because tendons get so little blood flow compared with muscles, my injury might take longer to heal than a similar strain in the middle of the hamstring.

But I'm on the mend -- physical therapy, including heat, electric stimulation, stretching, strengthening and ice -- and have already sworn to return to regular yoga practice, which I'd dropped in recent years, as soon as I'm able. That will strengthen and elongate the fibers of my hamstring (along with connective tissues and other muscles).

For fans of more traditional regimens, two good exercises that benefit both quads and hamstrings, ensuring they stay in approximate balance: the lunge (with dumbbells or without; make sure your knee does not pass beyond your toes!); and the step-up (onto a low bench or step). Standing farther away from the step shifts focus more to the hamstring.

Some people tell me injuries like this are a sign I need to slow down. To them, I'd like to quote my leg: No way, Jack.

No chat today; e-mail is move@washpost.com .

-- John Briley