Physiology Friday Issue #9: Are Today’s Youth Aerobically Unfit? + Heat Therapy for Cardiometabolic Health

Brady Holmer
4 min readApr 15, 2022


Hello friends,

Happy Physiology Friday!

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Are today’s young adults unhealthier than ever?

Earlier this week, Dr. Tamara Hew-Butler (who has appeared on my podcast and is an awesome scientist and all-around person) presented some “unofficial” data on her Twitter account that caused quite a stir.

She explained how, during some mandatory aerobic fitness (VO2 max) tests in her undergraduate exercise physiology class, values for the students were astoundingly low — with scores of 31.2 ml/kg/min on average. For males, the class average was ~43 ml/kg/min and for females, 34 ml/kg/min. To put that in perspective, this means most males in the class fall into the “below average” to “average” category of VO2 max and most females fall into the “below average” category (charts from:

In addition to having poor fitness, the peak speed at which the female students reached their theoretical “max” exercise capacity was 7 miles per hour — that’s a brisk walk! For males, the peak speed was an unremarkable 9 miles per hour.

In a final follow-up tweet, Dr. Hew-Butler remarked how their data also apparently refute a commonly-held idea that one can be “fit but fat” by showing that VO2 max and body fat seemed to be highly correlated among students in the class — with higher body fat % being associated with lower aerobic fitness levels and little evidence to support otherwise, even among the individual-level data (i.e. no students with high body fat and high aerobic fitness levels).

There is a commonly cited statistic that only about 12% of Americans are “metabolically healthy.” While I think this number may be inflated, data like those above are somewhat concerning and perhaps support that we are in a pandemic of metabolic disease. These students — who we might assume are into fitness and exercise (they were part of an undergraduate exercise physiology class) — displayed somewhat poor aerobic fitness levels and elevated body fat. Is the metabolic and cardiorespiratory health of younger generations on the decline? If so, what could explain this?

COVID may have played a role, but Dr. Hew-Butler also noted no differences in pre- and post-pandemic VO2 max values for her students! More than likely, the situation is the same as it is for older adults throughout our country and the world — a lack of physical activity!

Should PE be mandated as Dr. Hew-Butler’s tweets might suggest? It doesn’t seem too out of this world of an idea and might be especially pertinent to begin promoting fitness in elementary-aged children who can then begin life on an upward trajectory.

A high aerobic fitness enhances quality of life, reduces the risk for frailty and cardiovascular disease, and is highly correlated with longevity. Don’t neglect your VO2 max!

Could heat therapy help people with diabetes?

Exercise and diet are first-line strategies against the metabolic derangements of diabetes; which is characterized by high blood glucose levels secondary to insulin resistance. Could other less-intensive strategies also be effective for disease management?

A new study published ahead-of-print in the Journal of Applied Physiology investigated whether passive heat therapy could enhance blood glucose control and improve vascular function in individuals with type 2 diabetes.

1 hour of hot water immersion (41C/105F) had no effect on blood glucose control (insulin sensitivity) or measures of blood vessel function or any of the heat-shock proteins assessed in the study when compared to a thermoneutral (normal temperature) bath. This suggests that passive heat therapy may not be an effective or novel way to manage diabetes. Though the hypothesis was interesting, sitting in a hot bath for 60 minutes just might not be enough of a stimulus to improve cardiometabolic health.

I hope you enjoyed this week’s newsletter and, as always, thanks for reading!




Brady Holmer

PhD candidate at the University of Florida — Science writing with a particular focus on exercise and nutrition interventions, aging, health, and disease.