Glycogen Dethroned …?

A couple of weeks ago I wrote Running on Fat in which I said that glycogen was king. The current paradigm can be summed up as things go better with carbs. That is before during and after. Muscle glycogen depletion during  exercise is the main factor in the onset of fatigue.  If you want to exercise again in a hurry you need to get some carbs down in a hurry. The amount and type vary from paper to paper and there is an unresolved debate about the addition of protein. Overall though it is suggested that 6 to 12 grams of carbohydrate per kilogram within 30 minutes of completing an exhausting workout should have you ready to go again the next day.

Since my muscles are not being rewarded for their efforts with a jar of marmalade after every session I have been wondering how much of a disadvantage I’m putting them at. And it’s not that easy to find out.

Some short term research has been done putting normal (high carb) athletes on low carb diets for three weeks and watching their performance suffer. Hardly surprising that it goes down hill it takes a few weeks to sort out your fluid and electrolyte balance and adjust to ketosis.

The body can make it’s own glucose from fat and if it’s starving it can turn to protein. In the absence of ingested carbohydrate does glycogen replacement grind to a halt or does gluconeogenesis step into the breach?

I was pleased to come across a paper by Volek et al describing research with 20 well matched elite athletes 10 of whom were regular high carb guys and 10 were low carbers (and had been for at least 9 months). Naturally, when you get your hands on such a group, you take muscle biopsies and put them on a treadmill for three hours, take more muscle biopsies and measure everything you can think of. Then you give them two hours to recover before taking another muscle biopsy!

The rate of fat oxidation was two to three times higher in the low carb athletes and it peaked at a higher level of effort. Glycogen stores, usage and replacement were very much the same in both groups.

Their conclusion …

Compared to highly trained ultra-endurance athletes consuming an HC (High Carb) diet, long-term keto-adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.

At the ultra marathon level the benefits of using fat as fuel are appealing to more and more competitors, you just don’t run out.

Stretch …

This article does not concern itself with my impact on Lycra. The world is not yet ready for that experience, getting there though. No, today’s analysis concerns the enormous benefit the cyclist can expect from stretching.

Athletes stretch for a number of reasons principally

  • to enhance athletic performance
  • prevent injury
  • prevent muscle soreness
  • improve flexibility

Let’s deal with the last first because this is purely an opinion. If you search for bike fit on Youtube you will be able to occupy hours of your time, hear the word flexibility frequently, learn the importance of a professional bike fit and learn virtually nothing about how to do it for yourself.

How much flexibility does a cyclist need? If you can bend at the waist, stretch your arms out in front and send your feet once round the pedals you’ve got it. What’s more repeating it will not increase it. Strength and stamina will help you keep at it longer but that comes from training not stretching.

So flexibility is not high on my list of concerns but I would definitely like to perform better whilst avoiding injury and muscle soreness.

Esposito and Limonta investigated the effect of passive stretching on performance. Nine males exercised at 85% of VO2max until exhaustion with and without pre-exercise stretching. A good stretch prior to exercise decreased endurance by 26%,  increased the oxygen needed by 4% and decreased efficiency by 4%. No, I haven’t reported the results round the wrong way …

These results are suggestive of an impairment in cycling efficiency due to changes in muscle neural activation and viscoelastic characteristics induced by stretching.

It’s not an isolated finding. Here’s another Wilson et al. It also goes for sprinting but here’s some good news – dynamic stretching doesn’t hinder athletic performance as much!

It might be worth sacrificing some performance for insurance against injury. Pope et al

investigated the effect of muscle stretching during warm-up on the risk of exercise-related injury. 1538 male army recruits were randomly allocated to stretch or control groups. During the ensuing 12 wk of training, both groups performed active warm-up exercises before physical training sessions. In addition, the stretch group performed one 20-s static stretch under supervision for each of six major leg muscle groups during every warm-up. The control group did not stretch.

The protective benefit? Nil.

Muscle soreness has been investigated sufficiently often for there to be a Cochrane meta-analysis on the subject. Twelve studies including over 12,000 participants were included in the review. The conclusions …

The evidence from randomised studies suggests that muscle stretching, whether conducted before, after, or before and after exercise, does not produce clinically important reductions in delayed‐onset muscle soreness in healthy adults.

So there you have it. If you see people stretching before your next race or charity ride give them a a few words of encouragement and a big smile.