It’s time for your weekend long run. Before heading out, do you fuel up with a bowl of cereal or a fruit smoothie? Rev-up with a cup of coffee or espresso shot? Or just grab your water bottle and hit the road on empty? Along with sleep, a proper training regimen, and adequate recovery, our choice of pre-run fuel is perhaps one of the most critical factors in determining how we perform, both on today’s run and years into the future.
Train low, race high
An increasing number of runners are adhering to the “train low, race high” tactic. This involves performing training runs with diminished glucose reserves, often achieved through fasting or completing back-to-back workouts, but restoring glucose levels through rest and carbohydrate intake for competition. Earlier research 1,2 has shown that this technique induces positive training adaptations, mediated by altered cell signaling and transcriptional regulation of proteins involved in muscle cell metabolism. These studies provide some evidence, albeit limited and inconclusive, that these metabolic changes may improve performance over time. However, training low is not without its drawbacks, as any runner who’s hit the wall from low blood sugar can attest. If only we could reap the long-term metabolic benefits of low-energy training without the immediate battle with fatigue and premature bonking. A new study suggests that caffeine just may be the secret ingredient that allows endurance athletes to have their cake – without eating it too.
Caffeine to the rescue
In their study 3, Stephen Lane and colleagues tested how caffeine and the availability of glycogen, which is broken down into glucose as our muscles’ main energy source, interactively affect cycling performance. Twelve trained endurance cyclists completed four test sessions each. At each session, the participants completed high-intensity-interval training, consisting of eight five-minute trials at maximal cycling intensity. The researchers monitored heart rate, power output, cadence and perceived exertion, as well as collected blood samples to measure glucose and free fatty acid levels. At each session, the cyclists were randomly assigned to a low- or high-glycogen condition, and a caffeine or placebo condition. Participants completed a 100-minute cycling session either two hours before testing, to deplete muscle glycogen (low condition), or 24 hours before testing, to allow sufficient recovery of glycogen levels (high condition). Then, an hour before each test trial, the cyclists took either 3 mg/kg caffeine, approximately 200 mg for a 150 pound individual (the equivalent of a cup of coffee), or a placebo pill.
As expected, when the cyclists’ muscle glycogen was depleted, their cycling power output was reduced by about 8% compared to when they cycled with normal glycogen levels. Critically, regardless of glycogen availability, caffeine improved power output by about 3%, and the effects of caffeine and glycogen did not interact (i.e. they did not influence one another). Note that caffeine couldn’t completely compensate for the performance deficit induced by glycogen depletion, but any boost is still a boost!
We’ve long known that carbohydrates and caffeine are both performance enhancers 4,5, so what’s so novel about this finding? One possible explanation for caffeine’s benefits is that it somehow improves performance by facilitating carbohydrate use, in which case caffeine might fail miserably at increasing performance when glycogen is low. But intriguingly, the study showed that the energy boost from caffeine does not depend on glycogen levels, so you can still get that performance bump while training on empty. If caffeine’s effects aren’t in fact mediated by carbohydrate metabolism, what energy source does it tap into? Interestingly, the researchers found that free fatty acid levels were elevated after caffeine consumption, suggesting that caffeine might allow muscles to more efficiently metabolize fats, rather than rely on muscle glycogen stores.
As the authors point out, their findings only show immediate performance perks from caffeine, and don’t inform about how caffeine influences the known long-term metabolic adaptations induced by low-energy training. Follow-up studies will also be necessary to show whether caffeine has similar effects when energy stores are depleted through fasting, rather than through repeat workouts. As a distance runner, I would be particularly interested in seeing whether these effects hold up during running, as well as during more prolonged bouts of endurance testing.
So if you’re looking to run hard and feel great, a granola bar and coffee might be a match made in heaven. However, if your goal is to stay strong while gaining long-term improvements in metabolic efficiency, a cup of joe might be all you need.
- Hansen AK et al. 2005. Skeletal muscle adaptation: training twice every second day vs. training once daily. J Appl Physiol 98:93-9.
- Hawley JA & Burke LM. 2010. Carbohydrate availability and training adaptation: effects on cell metabolism. Exerc Sport Sci Rev 38:152-60.
- Lane SC et al. 2013. Caffeine Ingestion and Cycling Power Output in a Low or Normal Muscle Glycogen State. Med Sci Sports Exerc.
- Graham TE & Spriet LL. 1995. Metabolic, catecholamine, and exercise performance responses to various doses of caffeine. J Appl Physiol 78:867-74.
- Jeukendrup AE. 2004. Carbohydrate intake during exercise and performance. Nutrition 20:669-77.
Lane, S., Areta, J., Bird, S., Coffey, V., Burke, L., Desbrow, B., Karagounis, L., & Hawley, J. (2013). Caffeine Ingestion and Cycling Power Output in a Low or Normal Muscle Glycogen State Medicine & Science in Sports & Exercise DOI: 10.1249/MSS.0b013e31828af183