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Science of Sport: Sore No More

By Owen Anderson, Ph. D. (Copyright © 2004-2006)

It has happened to you: You’ve gone out for an extra-long run, worked out on some steep hills for the very first time, or completed an unusual number of work intervals on the track – and then paid the price. For a few days after your effort, your legs felt stiff, your muscles were tender and sore, and your usual leg strength was missing in action.

It's also very likely that you had an interesting, follow-up experience with soreness, or lack of same. That is, you probably performed – at a later date - a workout similar to the one which produced so much leg distress initially. Somewhat surprisingly, this second session produced no ill effects at all – not even a whisper of protest from the sinews and cables in your lower appendages. Why did the first effort lead to misfortune, while the second failed to perturb your legs at all?

This scenario, in which a specific workout produces pain after its initial completion and then rubs milk-and-honey balm on your legs after its second and subsequent fulfillments, has been noticed by exercise scientists and is often called the “repeated-bout effect”. Amazingly enough, the “protection” from soreness and enfeeblement which occurs after the first training session can last for several weeks – and possibly for as long as six months in some cases.

Why should we care about this? If we can understand the underlying mechanism which produces protection from significant soreness, it might be possible train in ways which invoke this mechanism (without producing significant tissue damage) and thus protect ourselves from muscle strains and training-related tendon damage. There might, in fact, be a general routine, a combination of strength training and running, which, when carried out during an initial phase of training, could provide many protective benefits over the course of a training year.

Research concerning the repeated-bout effect has produced many surprises. One shocker is that a muscle group does not have to be exercised in the same manner in the initial and subsequent bouts of exertion in order for a protective effect to occur (a clear violation of the specificity-of-training principle). One study, for example, found that 100 maximal, eccentric contractions of the quadriceps muscles, carried out with a static body position, furnished protection against quadriceps damage following a subsequent bout of vigorous downhill running.

Note that I said "eccentric" contractions of the quadriceps muscles. Recall that eccentric muscle contractions are notorious for producing soreness and that an eccentric muscular contraction is one in which a muscle is exerting force and attempting to shorten – and yet ends up being elongated by other forces acting on the muscle.

A good example of this is what happens to your quads as you run. The poor fellows contract when your foot hits the ground, but the forces of impact make your knee flex anyway, and the quads get temporarily stretched and lengthened – as they are trying to shorten and keep the knee joint under control. Put yourself on a significant hill and run in a downward direction – and things get much worse for the quads. Since your foot is falling farther with each step, the leg is accelerating downward to a greater extent than usual, and thus the forces on the quads are considerably augmented. The eccentric-strain damage to the quads is more extensive, and post-workout quadriceps pain is likely to appear – if you have not done much prior downhill running.

It is clear that eccentric strains produce a significant amount of the leg discomfort which is part of running training. However, there is also something about eccentric straining/training which ultimately provides a considerable amount of protection for muscles and tendons. In short, eccentric strains damage muscles – but lead to adaptations which are highly protective.

Interestingly enough, the intensity of the initial bout of exercise must be close to maximal in order to provide protection – if subsequent efforts also involve close-to-max intensities. In one piece of research, eight weeks of eccentric training at very moderate intensities of about 50 percent of the one-repetition maximum (i. e., 50 percent of the heaviest weight which could be utilized for the successful completion of one movement) produced no protection at all for a workout involving maximal eccentric exercise.

One of the proposed mechanisms which has been advanced to explain the repeated-bouts effect is the neural-adaptation theory. This theory suggests that it is the nervous system, not the muscular system, which is to blame for the soreness associated with the first workout, and that the nervous system then adopts a new method of controlling muscles which protects against damage during similar, subsequent training sessions.

The neural-adaptation theory is attractive for a number of reasons. First, it has been known for a long time that eccentric contractions involve less motor-unit activation for a given muscle force, compared with concentric and isometric contractions. This is a slightly bad thing in one way, because it means that each involved muscle fiber is acted upon by a greater force during an eccentric contraction (a given level of force is spread over a smaller number of fibers, heightening the force per fiber). This suggests that it is easier for muscle cells to get damaged during an eccentric contraction, and one can point the finger of blame at the nervous system. Why isn’t it recruiting more muscle cells to stand up to eccentric strains?

It is also known that eccentric contractions lead to the preferential recruitment of fast-twitch muscle cells, compared with concentric contractions, which tend to rely more heavily on slow-twitch muscle fibers. Unfortunately, research has shown that fast-twitch fibers are more susceptible to disruption as a result of eccentric contractions (compared with slow-twitchers). This may be because fast-twitch cells shorten more quickly than slow-twitch fibers (as their names suggest), and thus the rate of increase of strain is greater in fast-twitchers, or it may simply be that eccentric contractions are damaging, no matter what kind of muscle cell is involved, and that fast-twitches are recruited by the nervous system and thus have to bear the brunt of the damage.

At any rate, it has been proposed that an initial episode of eccentric strain “teaches” the nervous system to increase its recruitment of slow-twitch muscle fibers during subsequent efforts. In other words, a premier bout of damaging exercise might stimulate the nervous system to do a better job (subsequently) of spreading the workload around among additional fibers, including slow-twitch cells. The fast-twitchers would no longer have to handle the whole load, and thus the strain per fiber would be reduced.

There is evidence to support this idea. For example, one of the effects of systematic, eccentric strength training is an increase in the amplitude of the surface electromyography (EMG) signal of the muscles which are being trained, indicating that a greater number of fibers are being recruited to carry out the work. In addition, some research has shown that there is a decrease in the frequency content of the EMG signal in the second bout of exercise (i. e., the nervous system is stimulating the muscles less often), which suggests that there is an increased recruitment of slow-twitch cells taking place. The decrease in frequency content might also signify a great synchronization of motor-unit firing, but either way a neural adaptation would be required.

Unfortunately (for neural-adaptation-theory protagonists), it is clear that a protective effect can occur over repeated bouts of exercise without any neural adaptation at all. In some research, the nervous system has been taken completely out of the picture, with eccentric contractions induced via external electric stimulation, and yet the repeated-bout effect still occurs. For example, in a study carried out using elbow-flexor muscles, an initial bout of electrically stimulated eccentric contractions produced a major drop-off in elbow-flexor strength, a loss of muscle tone, major swelling, significant soreness, and an elevation of blood-plasma concentrations of muscle enzymes which are often linked with muscle damage. Two weeks later, the electrical stimulation of the muscles was repeated, but this time there was little damage. Since the central nervous system was not involved to any significant degree in the work carried out by the elbow-flexors in either workout (the muscle cells were stimulated electrically rather than by neurons), the investigators in this study were forced to conclude that “peripheral adaptations” (changes accomplished outside of the nervous system) probably play the most-important role in producing the repeated-bouts effect.”

While the exact mechanism underlying the repeated-bouts effect is unknown at this time, it is still possible to outline the exercises which will virtually eliminate soreness in your leg muscles – the exertions which have an amazingly protective effect for the key muscles in your lower limbs. We don’t know exactly how these movements work – we only know that they provide your legs with a sturdy soreness shelter. The muscles which get sore most commonly are the quads, the glute/hamstring group, and the calves, and we have protective movements for each.

To safeguard your glutes and hamstrings, for example, please carry out the following two exercises:

(1) High-Bench Step-Ups: Begin from a standing position on top of a six- to eight-inch high bench or step, with your body weight on your left foot and your weight shifted toward your left heel. Your right foot should be free and held slightly behind your body. Lower your body in a controlled manner until the toes of your right foot touch the ground behind the bench or step, but continue to support all of your weight on your left foot (the touch with your right toes is very light). Then, push downward on the bench or step with your left foot and straighten your left leg; as you do this, swing your right leg upward and forward until your right thigh is parallel with the surface of the bench or step. As your right thigh swings upward, your right leg should be bent at the knee, and your left arm should swing forward naturally as your right leg swings up and ahead. Hold the right-thigh-up position for a moment (completing one rep), and then slowly and smoothly lower your right toes to the ground behind the bench or step, starting your second repetition. Continue in this manner for the prescribed number of reps (see below), and then switch over and complete the same number of repetitions with your right leg bearing your weight (while your left foot drops behind you). Maintain upright posture with your trunk throughout the whole movement. As you get stronger and more-controlled with this exercise, progress to a higher bench or step.

(2) Straight-Leg Dead Lifts (thanks to Karen Ward for providing proper form): From a standing position, please hold 10-lb dumbbells in each hand, with your arms hanging naturally at your side, toward the ground. Your body should be in proper, kinetic-chain alignment: Your feet are parallel and your arches are lifted, your knees are pointed straight-ahead, your quads are slightly contracted, your glutes are lightly contracted, your abs are pulled in, your low back is in neutral position (your spine has a natural curve inward, but not an exaggerated one), your ribs are in neutral position (not rotated up, which would cause the upper back to lean backward, nor rotated down, which would produce a hunched-over position), your shoulder blades are retracted (pulled together and slightly down, which pulls the head of each humerus into the shoulder socket), and your head is pulled back slightly so that is in alignment with your body and is held in a neutral position (as though you were balancing a book on top of your head). This starting position is a bit of an exercise in itself!

Now, at last, here’s the dead-lift movement: Bend forward only at your hip joints by shifting the hips (butt) back while keeping the natural alignment of your spine and while keeping your shoulder blades retracted. If your hamstrings or glutes are quite tight, the range of motion may be small, but that’s OK initially. Don’t push forward into what is a painful position. After bending forward, return to the standing, erect, starting position by actively contracting your glutes and hams. As you carry out the full dead-lift movement, be careful not to let your shoulder blades move to the outside, and be certain not to round your lower back like a scared dog.

And the May 2006 issue of Running Research News covers the topic of soreness in complete detail and tells you how to keep your quads, calves, and Achilles tendons out of trouble.

Please visit our web site at www.runningresearchnews.com to get the latest information about training, sports nutrition, and injury prevention.

Copyright © 2006 Running Research News, All rights reserved. Posted with permission.

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