Obesity Negates Glucose Sensitizing Effects of Resistance Training. Lifting Works Only For Normal Weight Women

The results of the study at hand clearly suggest: There is no single ideal type of exercise; plus: What's optimal may change when your health / physique changes
"You got to exercise!" When the average overweight patient hears these words coming out of the mouth of his doctor, the type of exercise he usually will be thinking about is "classic" steady state cardio training on a treadmill, elliptical, stairmaster, or ergometer.

It's the textbook approach and still the predominant form of exercise in most of the pertinent studies on nutrition + exercise interventions that are designed to help overweight / obese individuals shed weight and improve their health.

Among the (usually) non-obese and rarely insulin resistant members of the health and fitness community this type of "cardio training" (LISS) has however gotten quite a bad rep as of late.

More and more trainers suggest that it may bet better to lift weights and do the occasional HIIT sessions for everyone - irrespective of your body weight, health and training status. If we put some faith into the results of a recently published study from the University of Massachusetts this could eventually turn out to be another unwarranted over-generalization that disregards the very specific needs of lean vs. obese and insulin sensitive vs. insulin resistant individuals.
Don't forget you are "evolving": Your journey from fat to fit will not simply change the way you look and feel, it will also have a direct impact on the optimal workout and nutrition regimen for you. Consider it your personal "evolution" that may well start out with a no-carb + endurance approach and "evolve" into a medium-to-high-carb + resistance training approach over the years.
Much contrary to the idea that there must be a perfect way to exercise, Steven K. Malin and his colleagues started out with the hypothesis that
"[...] excess body fat would attenuate the improvement in insulin sensitivity and reduction in glucose-stimulated insulin secretion after acute and chronic resistance exercise" (Malin. 2013)
In other words: The same type of exercise that may be highly beneficial for a lean / normal-weight individual could be absolutely ineffective for his overweight neighbor; and if that were the case, this would at least partly explain why some of the studies in obese individuals suggest that regular strength training would not be a match for the arduous light intensity steady stead training (LISS) approach to fitness.

Despite the fact that the corresponding control group on a LISS regimen was missing in the study at hand, the results Malin et al. present in their soon-to-be-published paper would in fact support just that: As long as you are still fat, weight training may be a good way to maintain lean body mass, but not the appropriate form of exercise to get your blood sugar problems and other health issues under control.

Body fat and pumping iron don't groove

The subjects of the Malin's study were 26 young women (21.2±0.7 years) who ere randomized to either a control or intervention group.

Potential explanation of the phenomenon: In the obese the increase in free fatty acids due to the "stressing" (=sympathetic nervous system activity) effects of weight lifting may impair / reverse the exercise induced increase in glucose uptake.
Weights don't work for HDL, either! The beneficial effects of resistance training on HDL are blunted by obesity, too (Nicklas. 1997; study in men).
While the women in the control group had to do nothing but be their lazy sedentary selves, the (un?)lucky girls in the intervention group performed a classic progressive resistance training (PRT) with the following characteristics:
  • fully supervised exercise sessions 
  • 3 days/week for 7 weeks
  • workout duration ~60 min/session 
  • intensity 60 % 1-RM
  • 3 set of 8-12 repetitions
  • 90-120s rest between sets
  • 5-10 min of stretching before + after
Otherwise the women in the strength training arm of the study were instructed to maintain habitual physical activity and diet habits throughout the study...

... with one exception, though: On the day before the metabolic testing sessions, they were yet advised to consume a standardized mixedmeal diet with 55% carbohydrate, 30% fat, 15% protein.
Figure 1: Changes in glucose metabolism in response to exercise intervention (Malin. 2013)
With the standardized diets, it was thus not possible that the results in figure 1 (no improvement in insulin sensitivity in the obese women with a mean body fat percentage of 48.2%) were corrupted by crazy candy feasts on the day before.
Could "cardio" really be more than just a necessary evil on your way to a physique like this? (learn more)
So is it weight loss before weights, then? While it is true that there are no direct beneficial effects of resistance training on insulin sensitivity in the obese, you would be ill advised to skip it all together.

Let's assume you can train four times a week. In that case you could progress from a 3:1 to a 1:3 endurance-to-resistance-training-ratio as you journey from obese to normal weight and insulin resistant to "normal" (you can also use a 2:1 LISS : HIIT ratio, but keep in mind that HIIT hits the sympathetic CNS, as well).

It is also possible to combine both, cardio and weights - specifically if you belong to the group of trainees who lack minimal strength (you can't do 10 push ups) and endurance (you cannot jog casually for at least 15min).

  • Malin SK, Hinnerichs KR, Echtenkamp BG, Evetovich TK, Engebretsen BJ. Effect of adiposity on insulin action after acute and chronic resistance exercise in non-diabetic women. Eur J Appl Physiol. 2013 Sep 27.
  • Nicklas BJ, Katzel LI, Busby-Whitehead J, Goldberg AP. Increases in high-density lipoprotein cholesterol with endurance exercise training are blunted in obese compared with lean men. Metabolism. 1997 May;46(5):556-61.
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