Charging up hills boosts leg-muscle strength and improves your running economy, but what about running down hills? If you carry out repeats on a neighborhood incline, you've got to jog back down the hill before you surge upward again. Does such downhill ambling do anything special for you - aside from giving your knees a good jarring?

Of course! As we have mentioned previously in the pages of Running Research News, downhill running can help prevent leg-muscle soreness, especially in the quadriceps muscles in the front of the thigh. Soreness often results when one's muscles are challenged by a greater-than-normal number of eccentric contractions, in which the muscles attempt to shorten while they are actually being elongated.

The "quads" are notorious soreheads, mainly because gravity pulls the knee downward (e.g., produces knee flexion) with every footstrike during the act of running. This flexing stretches out the quads at the exact time they are contracting (attempting to shorten) to prevent excessive knee flexion. The resulting, repetitive strain (which occurs about 90 times per minute per leg) can produce significant quadriceps-muscle damage. If you simply complete your usual volume of training, your quads have already adapted to that amount of strain and ordinarily don't protest too much. However, if you run more miles than you are accustomed to, your quads tend to complain quite loudly. If you have ever boosted your mileage quickly or run a marathon, you know the feeling.

Downhill running actually magnifies this eccentric, "pulling-apart" stress on the quads, because the leg "falls" a little farther than normal with each stride. Thus the accelaration of the leg is greater at impact (footstrike), and the forces which produce knee flexion are consequently greater. The quads, of course, are still trying to carry out their yeoman-like work of resisting knee flexion, but the stress on them is much higher. Microscopic tears in the quads' muscle fibers and connective tissues can occur, and considerable soreness can result.

That doesn't mean that downhill running is bad for you, though: In the long run, it is actually good, because those old quads of yours adapt fairly readily. Once they've been exposed to some downhill running, they'll be sore, sure, but if you run downhill a few weeks later, the quads will be considerably "tougher" - and less apt to get sore. In addition, if - after your downhill exposure - you run longer than usual on the flat, your quads will also be less likely to get hurt. The soreness protection gained from downslope running does seem to carry over to regular efforts. Down Hill

                                                             The Six-Week Factor

In fact, for yet-to-be-explained reasons, the soreness insurance provided by a single bout of downhill running can often last for six weeks or more. Several years ago, scientists at the University of Massachusetts asked 109 individuals to perform two sets of 35 maximal, eccentric contractions of the biceps muscle in the upper part of one arm. Basically, these eccentric contractions consisted of lowering a very heavy weight, which forced the biceps muscles to elongate as the weight was lowered at the same time they were attempting to shorten to stabilize the weight's movement.

After this unusual workout, biceps soreness and tightness peaked about two to three days later, and maximal swelling occurred a few days after that. Biceps strength declined immediately after the rigorous session and stayed below-par for 10 days.

However, when the individuals tried the same biceps routine six weeks later (with no intervening biceps training), there was appreciably less soreness and little loss of muscle strength. The biceps muscles were somehow protected from problems as a result of that initial eccentric session.

Interestingly enough, the protection didn't last much longer than six weeks. When a second group of subjects waited 10 weeks after their initial eccentric workout to stress their biceps again, their biceps were thrown into uncontrollable agony and lost most of their strength. What was going on? Why could the bicep "remember" what happened six weeks before - but not 10 weeks before?

The Massachusetts researchers speculated that a strenuous bout of eccentric exercise "teaches" the nervous system how to better control and distribute the forces that are acting on particular muscles. In theory, this lessens the strain on individual muscle fibers when eccentric activity tries to "tear them apart" - and thereby reduces muscle damage and consequent pain. Just as the nervous system can learn to do this, it can also forget, and this forgetting seems to take place after six to 10 weeks. Six-Week Factor

                                           Australian Rats Reveal Sarcomere Secrets

Nice theory, but does it really work that way? To check it out, scientists at Monash University in Australia asked 16 laboratory rats to work out on treadmills over a five-day period. Eight of these rats participated only in "uphill" (inclined) running, while the other eight ran only "downhill" (declined running). Actual workouts consisted of five-minute work intervals with 1.5-minutes recoveries, starting with three work intervals on the fifth day. Running speed during the work intervals was a rather modest 16 meters per minute. After five days, the rats' quadriceps muscles  were tested for strength and then biopsied.

A key finding was that the quadriceps muscle cells of the decline-trained rats contained almost 10-percent more sarcomeres per cell, compared to the quads of the inclined rodents. To understand what sarcomeres are, bear in mind that a muscle cell is a barrel-shaped structure, and each "barrel" is filled with several hundred to several thousand cyclindrical, threadlike structures called myofibrils. To picture this, simply imagine a pipe-shaped structure (the muscle cell) stuffed with countless numbers of small cylindrical wires (the myofibrils). Incidentally, when we say that a muscle cell is shaped like a pipe, we are referring to a section of cylindrical water pipe, not to a pipe used for smoking purposes.

The myofibrils themselves are composed of microscopic, cylindrical compartments laid end to end (picture tiny cyclinders or spools glued together at their ends to make one long cylinder). These compartments are called the sarcomeres, and within the sarcomeres are the proteins (filaments) which actually allow muscles to both shorten and elongate. As special filaments slide inward (toward the middles of the sarcomeres), the myofibrils and overall muscle cell shorten, but when the filaments slide outward, the muscle gets longer.

As mentioned, downhill running induced the muscle cells to add more sarcomere to their myofibrils. Why is this increase in number of sarcomeres beneficial, and how can it prevent muscle damage and soreness? Since muscle-cell length itself didn't change significantly as a result of the downhill running, the fact that there were more sarcomeres per muscle cell was elongating, each sarcomere in a downhill-trained muscle would have to elongate less, and thus each sarcomere would be less likely to sustain internal damage. Sarcomere Secrets

To learn more about how WHAT HAPPENS WHEN YOUR RUNNING GOES DOWNHILL (the full article can be read by purchasing Vol.14-6 of Running Research News) and many more running related topics, simply click-on the Back Issues link, and select the volume and issues number, from the drop-down menu. A subscription to Running Research News is another way to receive valuable information about running.