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“To our knowledge this is the first study to report an increase in oxidative potential and significant hypertrophy [the missing link in the Goreham study, our # 322] following resistance training.” Tang et al, Applied Physiology Nutrition and Metabolism, vol. 31, 2006

Muscle Carries Aerobic Punch

Many have believed that strength training builds muscle at the expense of aerobic conditioning. That it makes people bigger and stronger, but lowers their ability to resist fatigue. Exercise physiologists worried that resistance-trained muscles are lacking in mitochondria, the oxygen-processing powerhouses in skeletal muscle. While beneficial to bodybuilders and strength athletes, such adaptations might be deleterious to those with health problems or suffering from age-induced muscle wasting (sarcopenia). Exercise physiologists at McMaster University in Canada are exploring these concerns—and finding them wanting.

In 2006, Jason E. Tang, Joseph W. Hartman, and Stuart M. Phillips (Department of Kinesiology, Exercise Metabolism Research Group) investigated “whether or not resistance training induced hypertrophy would reduce the oxidative potential of skeletal muscle.” They focused primarily on mitochondrial function in resistance trained muscle mass. It is well known that aerobic exercise increases the size and number of skeletal muscle mitochondria. Less clear is the effect of resistance training on mitochondrial potential.

The details are, of necessity, technical, but the tenor and the results are clear as a bell.

In the Tang study, 12 young men participated in a 12 week resistance training program (whole body, 2-3 sets of 6-12 reps) designed to increase strength and build muscle. The researchers measured the effect of the training program on enzymes reflective of oxygen uptake capacity, including citrate synthase (CS) and β-oxidation (β-HAD), as well as markers of glucose phosphorylation (HK) and glycolysis (PFK).

CS, β-HAD, and HK are indicators of oxygen processing potential, whereas, the process of  glycolysis (PFK) plays a role in both aerobic and anaerobic metabolism (with and without oxygen); the limited number of studies examining the effect of resistance training on glycolysis have found it to increase or remain unchanged. The findings in this study are based primarily on changes in CS and β-HAD. CS is a marker of mitochondrial mass and oxidative capacity; β-HAD is a measure of fatty acid conversion within the mitochondria.

Tang and his colleagues expected that the muscle mass created by the resistance training program would maintain its oxygen uptake potential. That’s what they found. Resistance training didn’t compromise aerobic capacity, it actually made it better.

“Our results indicate…that muscle hypertrophy after 12 weeks of high-intensity, whole body, resistance training does not compromise muscle oxidative metabolic potential. Instead, as muscle fiber size increases so too does oxidative enzyme content…, such that muscle oxidative potential is improved after resistance training induced fiber hypertrophy,” Tang et al reported.

Specifically, strength increased an average of 46.5% for all exercises, fat-free muscle mass increased an average of 7.28 pounds, the activity of CS, β-HAD, and HK all increased significantly, while glycolysis (PFK) was not affected by training.

CS and β-HAD increased by 24% and 22%, respectively. Recall that CS is a marker of mitochondrial mass and β-HAD is a measure of fatty acid conversion within the mitochondria.

“Since the activity of these enzymes are expressed relative to total muscle protein content, these data suggest that the oxidative potential of skeletal muscle is improved following resistance training-induced muscle fiber hypertrophy,” Tang et al wrote.

”We conclude that resistance training provides a stimulus for improving muscle oxidative potential, as reflected by the increased activity of CS and β-HAD following resistance training induced hypertrophy,” Tang and colleagues reported in the journal Applied Physiology Nutrition and Metabolism, Vol. 31, 2006.

“To our knowledge this is the first study to report an increase in oxidative potential and significant hypertrophy following resistance training,” the researchers wrote in the “Discussion” portion of their report. “Previous studies have reported an increase in [oxidative potential], but have failed to demonstrate significant increases in muscle fiber size.”

Results Heralded by Sprint Study 

The authors suggested that their results should, perhaps, not come as a surprise in view of findings the previous year that “brief bouts of repeated high-intensity dynamic exercise [very hard 30 second sprints] can stimulate marked improvements in oxidative capacity after as little as 2 weeks of training…Taken together these findings illustrate how short-duration high-intensity exercise can stimulate adaptations in oxidative metabolism that have traditionally been associated with only endurance exercise.” (Kirsten Burgomaster and colleagues at McMaster University published their results with sprint intervals in the Journal of Applied Physiology (June 2005); see http://www.cbass.com/Sprintendurance.htm ).       

The estrangement between aerobic training (AT) and resistance training (RT) was beginning to thaw. Another plank was laid in the bridge between aerobic and strength training. “I think it’s fair to say that there is a lot more in common between AT and RT than we’ve been taught/thought,” Jason Tang’s colleague and senior researcher Stuart Phillips wrote in an email.

(The Goreham and Tang studies, taken together, make a powerful case for resistance training as an essential element in a program for total fitness. But there’s more. Exercise scientists were just getting started in this line of research; see our next article, # 324.)

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