November 2020

Is There a Gender Difference in How Runners Use Glycogen

Intuitively, it would be difficult to posit that male and female runners use glycogen differently at similar intensities in different environments and in similar muscles. Glycogen is stored sugar in the muscle (and liver) that is readily available for energy production. And fueling strategies center on ensuring sufficient glycogen through long training runs and races.

So some British researchers seemed to think it was possible since (1) running outdoors differs from treadmill running and (2) no prior studies looked at whether or not gender differences affect glycogen use or (3) or at how different muscles use glycogen under these criteria. They quantified glycogen use in the vastus lateralis (the muscle on the outer thigh) and the gastrocnemius (calf muscle) in 11 male and 10 female recreational runners, during and after a 10-mile road run (aerobic), an 8 x 800 m (very high intensity) and a 3 x 10 minute (moderately high intensity) outdoor track interval sessions.

A primer on cardio and substrate use: Aerobic, long-distance exercise uses a combination of fats and sugars (carbohydrates.) Middle-distance, moderately high intensity work uses more carbs than fats with higher production of lactic acid. Sprints are high intensity and produce more lactic acid because they don’t use sugars efficiently.

The results showed that steady-state running used higher amounts of glycogen overall, as expected.

Females generally don’t store as much muscle glycogen and therefore don’t use as much, which may lead to more lactic acid accumulation. And the calf seems to use more glycogen than the thigh muscle.

They conclude that the gender differences in glycogen usage probably should not impact fueling strategies for women other than to make sure you eat enough carbs.          

For more on running physiology, read the following blog posts here, here, here, and here.       

MSSE Sept. 2020

No Butts About It

All major body movements are initiated from the ground through feet, knees and hips. From there, the central core – the abdominals and lower back muscles – must brace accordingly to enable proper and sufficient upper body movements. But when it comes to running power and speed, the buck stops and starts at the gluteal muscles of the buttocks.

A Loughborough University (England) team studied the sizes of 23 lower body muscles using MRI.  They looked at 5 elite sprinters (with personal bests of 9.99 seconds/100 meters), 26 sub-elite and 11 healthy, untrained males. The inclusion of elite runners differentiates this from prior studies with similar intents.

What they found was that the hip extensors (glutes and hamstrings) were ~32% larger in elite sprinters even compared to sub-elite ones who averaged only 1-1.25 seconds slower in the 100.

Interestingly, the calf muscles of elite and sub-elite sprinters were similar in size despite being renowned for that mystical force called ‘spring’, as in spring in your step.

Since 44% of the variability in performance was explained by the size of the glutes alone, it was almost serendipitous that elite sprinters glutes were 45% larger than those of the sub-elites. This suggests that not all big butts are bad. It simply depends on whether it’s muscle or fat.              

MSSE Oct. 2020

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