Runners seldom hit the proverbial wall—that’s, fall dramatically off their unique tempo towards the tip of a race—in races of half-marathon distance and fewer. However it occurs on a regular basis in marathons. Why?
The prevailing perception has been that the wall happens when a runner depletes his or her very restricted reserves of glycogen, a carbohydrate-based gas supply for muscle contractions. The physique shops loads of glycogen to get by way of shorter races, however not all the time sufficient to ship runners to the end line of a marathon, particularly if their tempo is just too aggressive.
This common clarification for the phenomenon of the wall in marathon working has stood up pretty properly to scientific scrutiny. Nonetheless, some runners hit the wall sooner than others, and a few don’t hit it in any respect. Additionally, amongst these runners who escape the wall, some are in a position to do some at a lot quicker paces than others. Clearly, then, glycogen depletion is a extremely particular person matter. Given this actuality, what are the precise elements that decide the chance of glycogen depletion in marathons? And the way can these elements be used to foretell glycogen depletion for the person runner and thereby assist her or him select a marathon tempo that can keep away from the dreaded wall?
Benjamin Rapoport of the Massachusetts Institute of Know-how requested himself these questions and answered them by making a mathematical mannequin. He discovered that the first elements that decide how briskly and the way far a runner can run earlier than glycogen depletion happens are cardio capability (or VO2 max), the mass of the runner’s leg musculature relative to the mass of the remainder of the physique, and the focus of glycogen shops within the leg muscle tissues and liver.
– The upper an athlete’s cardio capability is, the quicker he can cowl 26.2 miles, supplied he has ample glycogen shops.
– The bigger the athlete’s leg muscle tissues are relative to his full physique mass, the upper would be the share of his VO2 max that he can maintain for 26.2 miles as a result of a decrease physique mass means a decrease power price of working and larger leg muscle tissues imply extra room to retailer glycogen.
– And, clearly, extra concentrated glycogen shops within the legs and liver enhance the runner’s absolute endurance vary. Coaching drastically will increase carbohydrate storage capability. Carbohydrate loading and tapering allow runners to take advantage of that full capability.
The formulation that Rapoport made on the premise of those guidelines yield some attention-grabbing insights. For instance, it helps to clarify why an excellent pacing technique is one of the best ways to keep away from the wall and full a marathon within the shortest time. It seems you employ up your glycogen shops quicker in case your tempo fluctuates above and beneath a sure common than in case your tempo holds regular at that common. One other attention-grabbing discovering is that, theoretically, some runners don’t have to carbo-load to keep away from the wall in marathons. They can retailer sufficient glycogen to go the complete 26.2 miles at their most sustainable velocity on any given day. Carbo-loading will solely give them additional reserves that they are going to by no means use. Rapoport’s mannequin will also be used to find out how a lot supplemental carbohydrate a person runner should devour throughout a marathon to “push again the wall” to the end line at a desired common tempo.
It’s fairly cool stuff. Nonetheless, it’s unlikely that it is possible for you to to virtually profit from all of this math. For to take action you might want to know your VO2 max, leg muscle mass, and leg muscle and liver glycogen concentrations, and my guess is that you simply don’t know any of those variables, and even the place to go to establish them.
However there’s an excellent larger drawback. Rapoport proceeds as if glycogen depletion had been the only real limiter of marathon efficiency; that is clearly not the case. Train physiology is extremely complicated. Scores of interdependent elements have an effect on efficiency capability. It’s unattainable to single out only one physiological issue and deal with it as a stand-in for the entire combine.
Take into account the truth that particular person marathon occasions could be very precisely predicted from 10Ok race occasions. Glycogen depletion doesn’t happen in skilled runners of any potential stage in a 10Ok race. But when marathon efficiency is fully glycogen dependent, how can or not it’s predicted from efficiency in a a lot shorter race that’s glycogen unbiased? It doesn’t make sense.
The one actually world indicator of efficiency capability is perceived effort. Perceived effort, or how arduous working feels after a specific amount of working at a sure tempo, is predicated on all the physiological elements that affect our limits, together with muscle glycogen depletion, dehydration, core physique temperature, blood lactate ranges, muscle injury ranges, and so forth. Because of this, there’ll by no means be a extra dependable option to tempo a race effort than by really feel. It’s not an ideal method, nevertheless it turns into increasingly dependable with expertise and it’ll all the time be extra dependable than some sophisticated mathematical system that focuses too narrowly on one piece of the puzzle.
I’m not saying Rapoport’s mannequin doesn’t make superb predictions. It does. I’m simply saying I might by no means need to use it instead of perceived effort to tempo a marathon. There are two causes for this. First, perceived effort can information a runner each step of the best way all through a race. However a predicted optimum tempo primarily based on Rapoport’s system is static. It will possibly’t show you how to cope with any surprises after the gun goes off. Second, perceived effort is what truly makes you decelerate once you hit the wall. Bonking happens at quite a lot of completely different muscle glycogen ranges. The connection between muscle glycogen focus and fatigue just isn’t constant, which is one positive signal that it’s not the one limiter of efficiency. However the relationship between perceived effort and train fatigue is completely constant. When a runner begins to decelerate “involuntarily” towards the tip of a race, his perceived effort stage is all the time maximal. So doesn’t it make sense to make use of perceived effort to keep away from this example?
In fact, one may ask why the wall is so widespread in marathons within the first place if perceived effort is so dependable. That’s a subject for an additional article.