Some of you maybe aware that my girlfriend Ciara completed her first marathon in Berlin in September, she did a fantastic time of 3:53 and managed to run a negative split of nearly 2 minutes. She crossed the line smiling and felt she could have kept going and feels training on empty helped her a lot. I did not specifically coach Ciara as she is member of Lucan Harriers and they have a great woman’s coach.

I did help Ciara with a couple of elements of her training plan, I gave her some advice such as to only run 3 times a week, i.e. 2 club sessions and her long run at the weekend. I encouraged her to cross train for a couple of session a week, so she did boxercise and attended my pilates class on a weekly basis.

One area I did advise her on was her nutrition, I had done some research on training on empty and glycogen depletion. Studies show that a small amount (about 20%) of your body’s glycogen (energy) is stored in your liver while a majority (about 80%) of your body’s glycogen stores are inter-muscular. The amount of glycogen stored in your liver is highly variable throughout the day depending on activity levels, when and what you last ate, and time of day. If you wake up and go for a run without eating it is safe to assume that your liver glycogen stores are very depleted. However, inter-muscular glycogen stores are far less variable and far more plentiful than liver glycogen stores and will be your body’s primary source of fuel for those early morning runs. On inter-muscular glycogen alone you can sustain hours (2+) of intense activity such as running before they are completely depleted.

In addition, a 2011 study by Karen Van Proeyen et al. investigated the effects of training in a glycogen depleted and glycogen-replenished state using twenty young male cyclists. The men were split into two groups, both of which had equivalent diets and training regimens. The first group did all of their training after an overnight fast, while the second group took a carbohydrate-rich breakfast about 90min before their daily training session (a 60-90min bike ride at a fairly hard pace in the morning). After six weeks of training, both groups had improved a similar amount on a 60-minute time trial. However, there were several changes in the “fasted” group that indicated that their bodies had adapted to more efficiently burn fat as fuel.

  • First, levels of enzymes associated with fat metabolism increased significantly in the group which trained after the overnight fast, but not in the group which had a large breakfast before training.
  •  Additionally, their fat utilization increased throughout a range of intensities. That is, they could maintain a given pace with less reliance on glycogen, enabling them to last longer in a race without hitting the wall.

Based on the above theory and study, I suggested to Ciara that she start doing her long runs on an empty stomach. I did not just have her start off running for 2 hours without eating. Ciara started to train on an empty stomach about 3 months before her marathon, we gradually increased the amount of time she would run for without eating. Most of you probably do something similar but the objective was to train her body to learn to burn fat as the primary source of energy, and then have some carbs while out on her run, thus replenishing her glycogen levels so she does not bonk but can be more efficient with her energy reserves.

Ciara experimented with different bars and gels, and choose powerbar jellys as her carb of choice, she started running for an hour before eating some jellys on her run. As her runs got longer so did the period of running on empty, over the course of her marathon training Ciara worked up to nearly 3hrs of running on an empty stomach and then had a jelly every 20min for the remainder of her run. When she returned from her run she would then have a recovery shake.

While this was not a very scientific experiment, Ciara does feel it enabled her to run longer without pre loading carbs the day of the marathon, she did not have to worry about nutrition for the marathon. On the day of the marathon she was aiming for 4hrs and started with the 4hr pacer, she ran for about 3hrs before starting to eat the jellys, she finished in 3:53 without bonking or hitting a wall, and ran a negative split of nearly 2 mins. While nutrition may not have been the only cause for a great first marathon, Ciara does feel that running on empty for her long sessions helped her run without bonking, stomach problems or worrying about nutrition on the day.

I also read that training on empty is really only applicable for endurance training and not your average 10km race, if for example you were planning on doing an ultra marathon you should be able to train your body to last up to 4 hrs or so on your fat reserves. Then if you want to kick on towards the end of a race, you have some carbs to give you an energy kick for the fast finish you want. If you would like to discuss this or other topics please contact me at Range of Motion Physical Therapy, Lucan, Co Dublin