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Running on empty

[This article originally appeared in the December 2001 issue of Northwest Runner magazine.]

Among the many post-race excuses I've heard or offered over the years, "I didn't train enough for this" is one of my favorites. I like this excuse because it implies a simple solution to one's running woes: just train more, and you'll perform better. Sometimes, however, a basic lack of training is not the problem. In this article, we'll review some other common culprits that could be holding you back: too much training, muscle damage, and dietary deficits.

Too much training

Overtraining has been defined as "any short term or long term condition in which there is an imbalance between exercise and recovery, resulting in severe and prolonged fatigue" (Kuipers & Keizer, Sports Medicine 6: 79-92, 1988). It has been the focus of many research studies in which athletes have been asked to drastically increase the duration and/or intensity of their workouts. In many of these studies, most (Costill et al., Medicine and Science in Sports and Exercise 23: 371-7, 1991; Lehmann et al., International Journal of Sports Medicine 12: 444-52, 1991; Fry et al., European Journal of Applied Physiology 64: 335-44, 1992; Jeukendrup et al., International Journal of Sports Medicine 13: 534-41, 1992; Snyder et al., Medicine and Science in Sports and Exercise 27: 1063-70, 1995; Hedelin et al., Medicine and Science in Sports and Exercise 32: 1480-4, 2000; Bosquet et al., European Journal of Applied Physiology 84: 107-14, 2001) or at least one third (Costill et al., Medicine and Science in Sports and Exercise 20: 249-54, 1988; Mackinnon et al., Medicine and Science in Sports and Exercise 29: 1637-45, 1997; Dressendorfer et al., Clinical Journal of Sport Medicine 10: 279-85, 2000) of the athletes studied experienced a drop-off in performance and/or were unable to complete the training expected of them. On the other hand, runners in the experiments of Lehmann et al. (European Journal of Applied Physiology 64: 169-77, 1992) and Billat et al. (Medicine and Science in Sports and Exercise 31: 156-63, 1999) tolerated large increments in high-intensity training without experiencing any drop-off in energy level or performance. These latter athletes did harder-than-normal training 3 to 4 times per week but also had 3 to 4 easy recovery days per week, whereas the subjects of the other studies had to complete harder- or longer-than-normal workouts for several consecutive days. Thus it is possible to do really hard workouts without getting overtrained provided that each hard workout is followed by an adequate recovery period.

The importance of recovery days during seasons of severe training was shown most clearly in a 272-day study of male race horses (Bruin et al., Journal of Applied Physiology 76: 1908-13, 1994) in which days of intense interval training were alternated with days of moderate "endurance running" (20 minutes at a heart rate of 140 beats per minute). The interval training was gradually made more and more difficult in an attempt to wear the horses out. Nevertheless, the horses did just fine until their "endurance running" workouts were changed to 20 minutes of running at a heart rate of 180. Within a few days of this adjustment, the horses became sluggish and irritable and could no longer consume their daily ration of food or complete the assigned training.

While tough workouts combined with insufficient recovery periods can lead to overtraining, it remains difficult to predict when a given individual is on the verge of breaking down (Bruin et al., Journal of Applied Physiology 76: 1908-13, 1994; Kuipers, Research Quarterly for Exercise and Sport 67 (3 Suppl): S65-9, 1996; Gastmann et al., Journal of Sports Medicine and Physical Fitness 38: 188-93, 1998). As summarized by Kuipers (1996), "All attempts to identify a reliable, specific and sensitive parameter for early staleness have failed. Usually, an overtraining syndrome is diagnosed by excluding other causes for underperformance." Thus overtraining may occur in spite of reasonable attempts to avoid it. When this happens, about all you can do is reduce your training load until the persistent fatigue subsides.

An interesting side note is that, according to most researchers, intense prolonged exercise is accompanied by an increased risk of illness whether or not the exercise ultimately leads to overtraining (Nieman, Medicine and Science in Sports and Exercise 26: 128-39, 1994; Mackinnon, Immunology and Cell Biology 78: 502-9, 2000). As an example, a survey of 2,311 Los Angeles marathon finishers found that these runners were six times more likely than control runners to come down with upper respiratory tract infections in the week following the race (Nieman et al., Journal of Sports Medicine and Physical Fitness 30: 316-28, 1990). Furthermore, the work of Foster (Medicine and Science in Sports and Exercise 30: 1164-68, 1998) suggests that each athlete has a personal training load threshold above which he/she is likely to get sick. While the statistical methods of that study were not particularly rigorous, its conclusion is consistent with my own anecdotal observation that I tend to get a cold whenever I try to run more than 65 miles per week.

Muscle damage

Muscle pain is a symptom of muscle damage (Armstrong, Medicine and Science in Sports and Exercise 16: 529-38, 1984). This fact is intuitively obvious to most of us; if our legs are really sore, we don't expect to be able to run fast. However, it is also important to realize that our muscles may be (temporarily) damaged and our performance impaired even if we are not in pain.

Muscle damage may result from any intense exercise to which one's muscles are not accustomed. Especially common are injuries due to eccentric muscle contractions, i.e., contractions in which the muscle is lengthened as it tries to contract, as occurs in the quads during downhill running. Such contractions often lead to muscle soreness; however, the data of Clarkson et al. (Medicine and Science in Sports and Exercise 24: 512-20, 1992) and Howell et al. (Journal of Physiology 464: 183-96, 1993) indicate that muscle function can remain below normal even after the soreness has dissipated. This situation may arise in the weeks following a marathon, since there is microscopic evidence of incomplete healing 3 to 4 weeks after the race (Warhol et al., American Journal of Pathology 118: 331-9, 1985), by which time most marathoners are no longer sore.

While even marathon-inflicted damage is ultimately repaired by the body (Warhol et al., American Journal of Pathology 118: 331-9, 1985), prudent training can sometimes prevent such damage from occurring in the first place. Research shows that muscle damage and soreness may be minimized by gradually acclimating the muscles to the specific exercise that would otherwise cause the damage (Armstrong, Medicine and Science in Sports and Exercise 16: 529-38, 1984; Miles & Clarkson, Journal of Sports Medicine and Physical Fitness 34: 203-16, 1994. For instance, brief bouts of downhill running will protect the quads from the potentially damaging effects of subsequent downhill runs. Likewise, doing some light lifting during one's first couple trips to the weight room will make subsequent visits less painful.

Dietary deficits

As discussed in previous columns, one's success in long workouts and races depends in part upon what one eats and drinks while exercising. However, the success of such endeavors also hinges on what is ingested in the days and hours beforehand. In particular, an insufficient daily intake of fluids and/or carbohydrates can make endurance exercise more difficult than it has to be.

Several investigators (Buskirk et al., Journal of Applied Physiology 12: 189-94, 1958; Saltin, Journal of Applied Physiology 19: 1114-8, 1964; Craig & Cummings, Journal of Applied Physiology 21: 670-4, 1966; Caldwell et al., Journal of Applied Physiology 57: 1018-23, 1984; Armstrong et al., Medicine and Science in Sports and Exercise 17: 456-61, 1985) have dehydrated their experimental subjects (by putting them in saunas or giving them diuretics) and then measured their exercise capacity. Most of these studies involved a loss of 3 to 7% of body weight prior to exercise, so it is not surprising that performance was impaired. However, Armstrong et al. (1985) showed that water losses of as little as 1.2 liters (equivalent to 1.6% of body weight in the subjects studied) could slow 5K race times by over a minute. While 1.2 liters may still sound like a lot, it's less than the 1.8 liters of fluid that a typical American drinks in one day (Kleiner, Journal of the American Dietetic Association 99: 200-6, 1999), so day-to-day fluctuations of this magnitude are not out of the question. To avoid dehydration-related problems, the American College of Sports Medicine recommends drinking about 500 milliliters of fluid about 2 hours before exercise "to promote adequate hydration and allow time for excretion of excess ingested water" (Convertino et al., Medicine and Science in Sports and Exercise 28: i-vii, 1996).

Another aspect of everyday sports nutrition concerns the intake of carbohydrates. A number of studies (e.g., Kirwan et al., Journal of Applied Physiology 65: 2601-6, 1988; Snyder et al., Medicine and Science in Sports and Exercise 30: 1146-50, 1998; Cheuvront, Sports Medicine 27: 213-28, 1999) suggest that inadequate daily carbohydrate consumption depletes the body's carb stores (i.e., glycogen), which in turn can be detrimental to workout and race performance. While there is some evidence that these problems may be mitigated after adaptation to a high-fat diet (Lambert et al., Journal of Sports Sciences 15: 315-24, 1997), they can be avoided altogether by simply giving the body the carbohydrates it craves. Therefore, as discussed by Cheuvront (Sports Medicine 27: 213-28, 1999; see also Sports Medicine 29: 289-94, 2000), low-carb regimens such as the "Zone" diet are generally considered inappropriate for endurance athletes.

Other factors

The above list of performance-impairing factors is by no means exhaustive. I personally have used many additional excuses -- nervousness, recent illness, lack of sleep, inappropriate pacing strategies, bad weather, etc. -- and if poor races come my way in the future, I will continue to use them. However, since these other variables have not been well-researched and/or are outside my area of expertise, I have refrained from discussing them in this column. Finally, the cliche that "each person is different" certainly applies here. It is ultimately the responsibility of each athlete to identify the problems to which he/she is vulnerable and, through trial and error, to discover how they may best be avoided.


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