Fat loss in athletes: why resistance isn’t futile

Is resistance training more important than previously thought for reducing body fat? SPB looks at brand new research…

The conventional thinking about fat loss and training is that steady-state moderate-intensity aerobic exercise is the best route to reducing body fat. There are two reasons for this; firstly, the amount of energy (calories) expended per hour during aerobic type activity such as running, swimming, cycling, rowing etc is relatively high – typically ranging from 600-1,000kcals per hour depending on athlete fitness and level of exertion⁽¹⁾. Since aerobic activity can be continued for a significant period of time (up to two hours or more), the total calorie burn can therefore be very significant.

The second reason is that as long as there's ample oxygen available to working muscles (ie the athlete is not working at or near his maximum oxygen uptake limit [VO2max]), fat oxidation can contribute a major proportion of this energy demand. For examp le, an athlete working at a moderate intensity of 60%VO2max can easily derive over 50% of energy requirements from fat oxidation. Indeed, this concept underlines the practice of fat-burning training sessions, where athletes train at an intensity that maximizes fat burning – so called ‘fatmax’ (see figure 1).

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Figure 1: Fat burning, Fatmax and exercise intensity

Fat oxidation is maximized at 60-65% VO2max and falls as exercise intensity increases (where carbohydrate becomes progressively more important).

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Do athletes need more?

While the importance of aerobic training for maintaining or reducing levels of body fat has been confirmed in numerous peer-reviewed studies (have you ever seen a fat ultra-marathon runner?), athletes frequently but anecdotally report that when resistance training is added to an existing program, further and significant fat losses are observed, which are greater than those occurring simply by adding in extra aerobic training. In other words, resistance training itself seems to provide an additional mechanism for fat loss. But is there any truth in this?

That resistance training in itself can improve body composition by increasing lean muscle mass and reducing body fat is not in doubt. A large systematic review study published earlier this year reviewed a large number of previous studies and concluded that all forms of resistance training, but particularly forms where resistance exercise were completed in rapid succession (eg circuit type training) significantly reduced fat mass⁽²⁾. But can resistance training play an additional fat-burning role when added to an endurance program?

Another systematic review study looked at data from 12 trials involving 555 younger subjects who undertook either concurrent aerobic plus added resistance exercise, or aerobic exercise alone in order to lose body fat and improve key measures of health⁽³⁾. Importantly, the exercise volumes were matched. It found the following:

• Compared with aerobic exercise alone, aerobic + resistance exercise resulted in greater reductions in fat mass.
• Aerobic + resistance exercise resulted in greater increases in lean body mass (muscle) compared to aerobic only.
• The benefits for aerobic + resistance training were larger for longer programs (over 24 weeks) – ie the benefits for aerobic + resistance training continued to accrue.
• Blood lipid profile, particular cholesterol, improved more in the aerobic + resistance trained participants compared to aerobic only.

This last point is interesting; in another study, research on individuals with high blood lipids who underwent aerobic training found that replacing 20% of the aerobic training with resistance training significantly improved blood lipid profiles over and above aerobic-only training⁽⁴⁾.

New findings on resistance training and fat burning

Although there’s evidence that adding in resistance training to an aerobic-only program can provide additional fat loss benefits, there’s never been any mechanistic explanation. An often cited reason is that since resistance training increases muscle mass and muscle tissue is very metabolically active compared to other tissues in the body, more calories are required to maintain equilibrium; if calorie intake is not increased, then some of the extra energy is derived from fat oxidation. However, this doesn’t explain why resistance training appears to lower body fat levels when lean muscle mass is not significantly increased by resistance training.

But now, a new study published in the Federation of American Societies for Experimental Biology, has thrown some light on this question, and makes for fascinating reading⁽⁵⁾. In this study, researchers from the Kentucky College of Medicine and College of Health Sciences studied the phenomenon whereby muscle cells undergoing mechanical loading (ie strenuous resistance exercise) release small particles called extracellular vesicles from the muscle cells. Without delving too much into the technicalities, the researchers discovered that not only were these vesicles released following resistance training, but that they contained a signalling molecule called ‘muscle-specific miR-1’.

Once circulating in the bloodstream, these vesicles and their cargo of miR-1 were preferentially taken up by fat cells, and once inside the fat cells, the miR-1 stimulated the fat cells to released stored fat and then upregulate fat burning. In short, these vesicles acted like biological messengers to help switch on fat burning in fat cells - regardless of any other type(s) of exercise that take place. The significance of these findings cannot be understated; for the first time ever, we have solid evidence for why resistance training seems to provide a whole new dimension (ie a completely different pathway) for activating fat burning, and one that can take place during periods of inactivity, after resistance training!

In summary

Strength training has numerous benefits for athletes such as injury reduction, gains in power, speed and strength, as well as increases in muscle efficiency during endurance exercise (less oxygen required to maintain a given pace – see this article). However, this latest research provides valuable evidence that when it comes to fat burning and fat reduction, resistance training is also able to activate a completely separate metabolic pathway, which means that athletes who add some resistance training into their existing training can expect additional fat loss/weight control benefits. This strategy could be particularly useful for circumstances where athletes may struggle to maintain their weight – eg during the off season or when inactive following an injury. It can also benefit athletes who need to maximize their power-to-weight ratio (see this article) by simultaneously increasing strength/power and reducing body fat!

References

1. Brian J Sharkey ‘Physiology of Fitness’ 3^rd edition, Human Kinetics Publishing 1990, p48 (fig 3.3)
2. Biology (Basel). 2021 Apr 28;10(5):377
3. Br J Sports Med. 2018 Feb;52(3):161-166
4. Appl Physiol Nutr Metab. 2021 Jan;46(1):69-76
5. FASEB J. 2021 Jun;35(6):e21644.