The 22 athletes were divided into two equal groups: a traditional hamstring curl (HC) group and a Nordic hamstring (NH) group. Both groups then began a 10-week training program. The HC athletes performed their hamstring curls on a traditional hamstring curl machine. During the eccentric phase (i.e., the lowering of the weight), the athletes used as little effort as possible, providing minimal resistance to the dropping of the weight.
The Nordic hamstring exercise was the same one used in the Norwegian School of Sport Science study described earlier. Each group completed about 23 hamstring workouts during the 10-week training period, and there was no difference in the total amount of other training carried out, including soccer training, strength training, and endurance running. Postworkout soreness remained fairly minimal with no real difference between groups—a plus for the NH athletes since eccentric exercise is often linked with the invocation of muscle pain—and there were no changes in hamstring flexibility in either the NH or HC subjects.
Over the course of the 10 weeks, the HC athletes did achieve significant gains in strength while performing concentric hamstring curl exercises, boosting their 10-rep maximal resistance to 45 kilograms (99 lb). However, when the two groups were compared for maximal torque during eccentric actions—the ones believed to cause most hamstring injuries—the NH athletes were absolutely dominant. In fact, there were no improvements at all in eccentric strength for the HC players while the Nordic hamstring subjects exhibited a major increase in eccentric strength. The NH athletes boosted maximal eccentric hamstring torque by 11 percent while HC participants failed to get any better.
This is an example of mode specificity, which means that if athletes train their muscles using eccentric activities, their eccentric strength will improve, but they should not expect gains in concentric strength. Likewise, focusing on concentric actions tends not to lead to much improvement in eccentric strength. Overall, the gain in strength is specific to the mode of muscle activity. That is probably why a separate study carried out with college students produced results similar to those found by Bahr and his colleagues. In the college research, 12 workouts that revolved around eccentric hamstring strengthening (two training sessions per week for 6 weeks) produced significantly greater gains in peak eccentric hamstring torque compared with the same number of workouts stressing concentric work for the hamstrings.16
Improving Eccentric Muscle Strength
There is a general consensus in the scientific community that a lack of muscular strength increases the risk of running injury,17-19 and research suggests that increasing the eccentric strength of key muscles in the legs is one of the best ways to raise the injury threshold.20 Eccentric activities, in which muscles are forced to elongate while they are simultaneously attempting to shorten, tend to be more damaging to muscles than concentric and isometric actions, and eccentric muscular activity is quite pronounced during running. For example, the hamstring muscles in each leg are exposed to eccentric strain approximately 90 times per minute as they attempt to control forward swing of the leg. The hamstrings become active and pull back on the leg as it moves forward during swing, but the leg moves ahead nonetheless, producing significant eccentric strain; the hams are literally pulled apart as they attempt to shorten.
Eccentric strengthening of the hamstrings should help them handle these tearing actions by enhancing neural control of hamstring eccentric activity and by fortifying individual muscle cells within the hamstrings, thus boosting their resistance to damage. A lack of eccentric strength should heighten the risk of injury. To upgrade eccentric strength of the hamstrings, runners should carry out the bicycle leg swings exercises first discussed in chapter 14 and addressed further in this chapter.
The other key muscle groups in the legs are also exposed to eccentric forces. The calf muscles (gastrocnemius and soleus) work eccentrically when their associated ankle goes through dorsiflexion during the stance phase of gait, and the quadriceps muscles in the front of the thigh work eccentrically during stance as the knee flexes naturally. The muscles on the bottom of the foot also work eccentrically during stance as the arch flattens after impact with the ground. Eccentric strengthening should thus have a wide-ranging impact on injury reduction, providing protection against many or all of the common running-related leg injuries.
To be most effective at preventing injury, exercises that feature eccentric actions for key muscle groups should be running specific. They should replicate the actions those muscles undergo during the gait cycle of running. Such exercises are not very difficult to design. The running-specific strengthening exercises described in chapter 14 all emphasize eccentric actions of the leg muscles during running-relevant movements. The bicycle leg swing (see chapter 14) is simple in conception but incorporates the exact kind of eccentric stress that is placed on the hamstrings during running; this exercise intensifies and expands that stress to produce a significant upswing in eccentric strength of the hamstrings.
Science and the 10 Percent Rule
One of the most popular strategies in the running community for preventing injury is the use of the 10 percent rule, which states that running volume should never increase by more than 10 percent from one week to the next. There is a certain logic to this dogma since it recognizes that an injury threshold exists and that runners should be wary about soaring above the threshold with their training plans. Ten percent would appear to be a reasonable governor of training-volume expansion since it permits training progressions to occur in seemingly reasonable increments.
Unfortunately, no scientific research has documented the benefits of the 10 percent dictum. The rule also has obvious problems. First, it focuses only on the distance run without taking training intensity, including running speed or percent O2max into account. Increasing volume by 10 percent from one week to the next while reducing intensity or holding it constant should place a different total stress on the leg muscles and connective tissues compared with augmenting volume by 10 percent and boosting intensity by 5 percent. It is possible that intensity should be temporarily decreased whenever volume increases although there has been little research in this area.
The 10 percent rule also fails to take into account workout types and may be overly conservative in some cases. An athlete who runs 5 miles (8 km) per workout three times a week without a hint of injury could probably boost volume by 20 percent (i.e., from 15 to 18 miles [24-29 km] per week) without significantly increasing injury risk by adding in a fourth workout of 3 miles (5 km) on another day of the week. In this case, the 10 percent rule is too conservative. The same athlete might run into trouble if he or she changed the schedule to two workouts of 9 miles (14 km) each per week even though the percent expansion of training volume would be the same. The 9-mile runs might have a more damaging effect on the legs because of the number of miles run in a state of significant fatigue than the combination of 5- and 3-mile sessions.
Another factor that should be considered is that expanding from 10 to 11 miles (16-18 km) per week probably is much easier to do without raising injury risk than increasing training from 50 to 55 miles (81-89 km) per week even though both moves involve a 10-percent change. The latter would add 5 miles per week—and thus more than 5,000 additional impacts with the ground per week—to legs already fairly heavily stressed by training. However, it could also be argued that the legs accustomed to running 50 miles (81 km) per week would be stronger and would thus be more prepared for the advancement compared with legs that can handle only 10 weekly miles (16 km).
Anecdotal evidence suggests that a too-rapid advance in training can increase the risk of injury dramatically. Nevertheless, the 10 percent rule appears to be too general and unscientific to be used successfully by the majority of runners. The rate at which a runner can increase his or her level of training is highly individualized, and it is up to each runner to recognize personal limits. Listening to one’s body and reducing volume or intensity at the first sign of lower-limb discomfort is an unscientific yet sound princ
iple to follow.
Massage and Other Options for Injury Prevention
Studies of running injuries imply that other practices in addition to eccentric strength training should also decrease the likelihood of running-related injury. As pointed out in chapter 21, improved recovery—including more sleep, better restoration of muscle glycogen between workouts, more rest days per week, and fewer consecutive days of training—is associated with a significantly lower risk of injury. Avoiding high-volume training, especially programs that soar above 40 miles (64 km) of running per week, is connected with less injury. No specific style or technique of running (e.g., the pose method or chi running) has been linked with a reduction in injury rate.
Massage is another practice that receives a lot of attention. Many runners and coaches believe that regular massage therapy reduces muscular soreness and tightness and thus helps to limit or prevent overuse injuries. Elite Kenyan runners in particular make massage a nearly mandatory component of their recovery regimes, which also include ample sleep, postworkout glycogen replenishment, and a high-carbohydrate diet; most top Kenyan runners believe that massage keeps the injury bug at bay.
What does science say about massage and injury? There is strong evidence that massage reduces muscle pain after intense or prolonged workouts, and recent research indicates that the therapeutic intervention can produce a number of positive effects on muscle cell functioning. In a study carried out at McMaster University, massage decreased inflammation and reduced the concentration of heat shock protein that is synthesized in muscles under stress in exercise-damaged muscles of young male subjects.23 Furthermore, massage was able to stimulate mitochondrial biogenesis, the enhanced production of the key energy-producing structures inside muscle fibers.
A separate inquiry carried out in China with animals has demonstrated that massage following muscle damage can increase the production of key proteins that are part of a muscle fiber’s cytoskeleton, which is the arrangement of force-producing structures and proteins inside the cell. The increase in these key proteins should help muscle cells restore themselves following damage.24
Despite popular perceptions, massage does not diminish lactate concentrations in muscles nor should it: Lactate is actually an important source of muscular energy. It appears that elite Kenyans are on the right track: Massage produces a number of effects that should help limit muscle trauma and promote recovery.
Icing for Pain Relief?
Although no one believes that icing can prevent injuries, many coaches and runners have faith in the notion that icing, or cryotherapy, is an effective method of treatment for muscles and connective tissues that have already been damaged, and that the intervention not only reduces pain but can also speed recovery. Research in this area is far from comprehensive and varies significantly in methodology and overall quality, but it appears that cryotherapy can be a fairly effective pain reducer for a variety of injuries.
However, there is very little evidence to suggest that icing leads to enhancement of range of motion or to improvement in muscular function following injury.21 In addition, excessive use of cryotherapy can occasionally produce nerve damage to iced areas of the body.22 Overall, icing seems to have little impact on the duration or quality of recovery following an overuse running injury.
Conclusion
Running-specific strength training, with an emphasis on movements that mimic the mechanics of running and thus have large eccentric components, is a key way to progress more quickly—and farther—with training without getting hurt; it thus represents an important mechanism for injury prevention. Optimal recovery is also crucial for injury avoidance, and postworkout stretching may also help prevent injuries. Gradual progressions in training probably temper the likelihood of injury compared with more aggressive increases in the volume and intensity of workouts. Other traditional injury-fighting strategies, including preworkout stretching and flexibility training, appear to have little impact on the risk of injury while running.
Chapter 41
Health Benefits of Running
Runners can expect to live about 5 years longer than couch potatoes.1 As epidemiologist Ralph Paffenbarger once said, “Each hour of running adds about two hours to a runner’s life.” A key reason for running’s salutary effect on longevity is that involvement in the sport reduces the risk of dying from the two major causes of mortality in developed countries: cardiovascular disease and cancer. In addition, running decreases the risks of developing lifespan-limiting disorders such as type 2 diabetes and high blood pressure; running also has positive effects on mental health and rates of obesity, and it limits the likelihood of becoming disabled.
Lowering the Risk of Coronary Heart Disease
The Health Professionals’ Follow-Up Study, carried out with 44,452 men between 1986 and 1998, found that there was an inverse relationship between running and the risk of coronary heart disease (CHD).2 In this research, there were 1,700 new cases of CHD over the course of 475,755 person years. Men who ran for just an hour or more per week, an average of only 8.6 minutes per day, had a 42 percent reduction in the risk of developing CHD compared with individuals who did not run at all. Strength training and rowing also produced reductions in CHD risk, but they tended to be smaller than the benefits associated with running.
A separate investigation, the Harvard Alumni Health Study, also found an inverse link between running and cardiovascular disease.3 The Harvard Study followed 12,516 middle-aged and older men (mean age 57.7 years, range 39-88 years) from 1977 through 1993; 2,135 cases of CHD occurred during this time period. Men who ran just 10 to 20 miles (16-32 km) per week enjoyed a 10 percent reduction in CHD risk; running more than 20 miles (32 km) weekly cut the likelihood of CHD by 20 percent.
Research indicates that running is also protective against CHD in women. In research carried out with 39,372 healthy female health professionals aged 45 years and older between 1992 and 1999, jogging or walking from 6 to 15 miles per week (10-24 km) trimmed the risk of CHD by about 45 percent.4
Importance of Total Energy Expenditure
The Harvard research revealed that workout duration was not an independent factor associated with CHD risk: Men who carried out longer workouts were not at lower risk of CHD than individuals whose training sessions were shorter as long as total energy expended during exercise was similar between the groups.5 To express this in another way, accumulated shorter sessions were just as valuable as longer sessions from the standpoint of preventing CHD as long as total distance was comparable.
The total amount of energy expended during running and other activities appears to be a key factor that protects against CHD: The more energy expended, the lower the risk even when the diet is somewhat atherogenic (i.e., high in saturated fat or low in antioxidants). This conclusion is supported by analyses of members of the Maasai tribe in Tanzania who follow a diet high in saturated fat and low in carbohydrates and antioxidants and yet have normal blood lipids and little evidence of cardiovascular disease.6 Maasai expend about 2,565 calories per day above their basal caloric requirements compared with an excess of just 1,500 calories in rural Bantu people who live near the Maasai and consume a nonatherogenic, high-carbohydrate, low-fat diet. Both groups have similar blood lipid profiles despite the Maasai’s preference for saturated fat.
It is important to note, however, that while running reduces the risk of CHD, it does not provide complete protection from the disease. Some marathon runners mistakenly believe that their protracted training programs make the probability of CHD infinitesimal.7 In a study carried out with 36 marathon runners who had suffered heart attacks, Timothy Noakes of the University of Cape Town found the average age of the stricken athletes to be 43.8 (range of 18-70) and mean marathon performance to be 3:28 (range of 2:33-4:28). Average training distance was 50 miles (81 km) per week, but several of the heart attack victims compiled 95 to 100 miles (153-161 km) of training weekly, and 16 of the 36 had finished at least one 90K (56 mi) ultramarathon.8 Nineteen of the
36 marathoners had received warnings of heart trouble prior to the actual attacks but had basically ignored them. The stricken runners tended to have a family history of heart disease, high LDL cholesterol levels, and high blood pressure although some of the individuals had none of these factors. It is clear that running effectively reduces the risk of CHD but is not an absolute barrier to the development of the disease.
Scientific investigations indicate that running may be helpful for those individuals already suffering from CHD. In an inquiry carried out with 2,137 men and 1,367 women with preexisting CHD, jogging just once a week was connected with a 20 percent reduction in the risk of death for men and a 32 percent drop for women compared with no exercise at all.9 Exercising more frequently further diminished the chances of dying from CHD.
Impact on Cholesterol Levels
One of the mechanisms by which running reduces the risk of CHD is the elevation of HDL, or good, cholesterol that is usually produced by regular training; other mechanisms include a reduction in blood pressure, drop in weight, and reduction in the blood’s tendency to form clots. Runners naturally wonder if there is an optimal level of running that heightens HDL cholesterol to the greatest possible extent.
Running Science Page 56
