“Sweat is just fat crying”. This motivational quote is seen on Instagram almost as much as Fat Loss Coaching Specialists. And much like the aforementioned online coaches, this quote is well-intentioned, but heavily misguided.

I spent years building my training around sweating as much as possible (stunning visual, you’re welcome), and assumed that unless I left the gym dripping in sweat, I had wasted my time and wouldn’t benefit from the session at all.

Time to dig a little deeper, and investigate – what makes a workout effective for fat loss?

What is Sweat?

One of the first steps to along our investigation is to identify what sweat actually is. Sweating is vital for thermoregulation – particularly with strenuous activity or in hot environments^[1]. During such conditions, it is essential to cool the body down to prevent heatstroke or heat exhaustion.

Many individuals also believe sweat plays a massive role in excretion – of waste, nutrients, and in some way-off cases – fat. This belief forms the rationale behind the marketing of many fitness fads – saunas to sweat out water weight, polar/heated chamber classes etc^[2]. However, as we will discover, this isn’t quite the case.

Sweat Glands

There are three main types of sweat glands:

• Eccrine
• Apocrine
• Apoeccrine^[2]

Eccrine glands are the most numerous, and are found close to the skin surface. Eccrine glands respond to changes in emotional state, in addition to responding to temperature changes. Eccrine sweat consists mostly of sodium and water^[2].

Apocrine glands are found primarily around the breast/skull/face. Apocrine sweat is primarily lipid dominant, but also contains protein, sugar and ammonia^[2]. Apoeccrine glands are largely contained within the axilla (armpit) area. Apoeccrine sweat is heavily sodium and water-based^[2].

Overall, sweat consists mostly of salt and water, with some small amounts of electrolytes. These are nowhere near the amounts excreted by dedicated excretory organs (kidneys).  

So, not all sweat is created equal, and it is not composed of last night’s Chinese takeaway that you’re currently trying to “sweat out”.

The Rate of Sweating

The rate at which we sweat is influenced by a number of different factors. Improved aerobic fitness and prolonged exposure to hot conditions are associated with more effective sweating response – read: you will sweat quicker, and cool down your body faster^[3].

Exercise intensity also increases the rate of sweating. Increased body mass is associated with higher rates of sweating, potentially due to the reduced capacity for exercise and increased metabolic output overall^[2].

Overall, if you want to sweat more – exercise at higher intensities, in hotter environments and have a higher body mass. Not the most practical, and as we will now discuss, not even necessary if fat loss is your goal.

How Do We Use Body Fat?

Excess energy in the body is stored in adipose tissue (fat tissue). This energy reserve is drawn on by the body to carry out activities of daily living and exercise. If you didn’t have any stored energy, you would be dead, and that makes for a bleak article.

Normal body fat percentage ranges are 13.4-21.7% for men, and 24.6-33.2% for women^[4]. However, it is important to note that this is unique to the individual, and metabolic health is so much more complex than body fat percentages. That’s a rant for a different day, but the important take home here is that body fat is essential for energy.

Triglycerides are stored in the adipose tissue. Triglycerides are broken down by the body to form fatty acids and glycerol. These are further metabolised to eventually form ATP. If mitochondria is the powerhouse of the cell, ATP is the fuel.

When we need more energy, such as during prolonged, intense exercise, our body can use these stored triglycerides to generate energy.

Sweating & Fat Loss/Calories Burned

By-products of lipid metabolism include carbon dioxide, water and ATP. You may recall from earlier, that sweat contains a high percentage of water. This has led many to draw the conclusion that sweating more indicates that the body is burning more fat, as you are producing more water. A reasonable assumption. But what does science say?

By now, hopefully you can appreciate that the answer is a hard no. Of course, sweating out a huge deal of water will cause you to lose weight. It is important to note here, as we discussed earlier, this is largely water.

Dehydration leads to a decrease in scale weight. This will be almost immediately reversed, once the individual rehydrates^[5].

So, if your goal is making weight for a competition, it makes sense to promote sweating to reduce this. If your goal is general fat loss or performance, breaking a sweat shouldn’t be a main focus.

So, How Do I Know If I Worked Hard Then?

If sweat is an unreliable metric, what can we use instead to measure intensity? There are a number of other measurements we can use, that are a lot more scientifically backed.

Rate of Perceived Exertion/Borg Scale

The Borg Rate of Perceived Exertion Scale (RPE) can be used to measure exercise intensity. The traditional Borg Scale runs from 6-20, but for ease we will discuss the Borg CR10 Scale. This scale runs from 0-10. A 0 indicates no exertion at all, and a 10 indicates maximum effort^[6].

You can use the RPE scale in aerobic training, to measure how hard you feel like you are working in your session.

Similarly, you can use RPE in your weight session, after each set, to determine how hard you felt it was.

It is important to note however, that the Borg/RPE scale is subjective. We are prone to overestimating our RPE, and we often have a lot more left in the tank than we think^[7]. However, it can be a good starting point!

Talk Test

The Talk Test is also a useful metric for aerobic exercise. It’s relatively easy to understand, use and practical. With healthy adults, during low-moderate intensity exercise, you should be able to speak a few sentences.

As intensity increases, your ability to speak decreases.

This method is well established in science, however it’s less useful for interval exercise^[8].

Reps In Reserve (RIR)

Reps In Reserve (RIR) is used in resistance training, and may be slightly more effective at determining intensity than RPE^[9]. The RIR scale is used to assess how many more repetitions an individual could perform in a set. It ranges from 1-10. At 10, you could perform no more reps, this is maximal effort. At 5-6, you could perform at least 4 more with good form. Below a 5, it is difficult to count how many more reps you could do.

Much like the RPE scale, this scale is subjective, and beginners may use it less accurately. It can be useful for the novice lifter, who is familiar with resistance training, and wants to monitor progress a little closer.

Objective Measurements: Heart Rate Tracking, HRV, V02 Max

We can also use more objective measurements to assess exercise intensity, such as measuring percentages of max heart rate, VO2 max or other metrics. In my opinion, for the novice trainer, they are not as important and detract from the training itself.

Constantly looking at your fitness watch during a run to make sure you’re running at 60% of your maximum heart rate is counter-productive, and if you’re running outside, it can even be dangerous (don’t want to crash into a tree do ya?).

I would argue that as you progress in your lifting or sport these measurements have their place, but if you’re not training for a competition or the Olympics, the subjective measurements will get you where you need to be without the bells and whistles.

Conclusion

Sweat happens. Chasing a sweat isn’t the most effective way to get results. You can monitor how “hard” you work through other, more reliable methods. And most importantly, sweat is most definitely not fat crying.

References

1. Casa, D.J., Cheuvront, S.N., Galloway, S.D., Shirreffs, S.M. (2019) ‘Fluid needs for Training, Competition, and Recovery in Track-and-Field Athletes’, International Journal of Sport Nutrition and Exercise Metabolism, 29(2), pp. 175-180.
2. Baker, L.B. (2019) ‘Physiology of sweat gland function: The roles of sweating and sweat composition in human health’, Temperature, 6(3), pp. 211-259.
3. Armstrong, L.E., Maresh, C.M. (1998) ‘Effects of Training, Environment, and Host Factors on the Sweating Response to Exercise’, International Journal of Sports Medicine, 19, pp. 103-105.
4. Kyle, U.G., Schutz, Y., Dupuertuis, Y.M., Pichard, C. (2003) ‘Body composition interpretation: Contributions of the fat-free mass index and the body fat mass index’, Nutrition, 19(7), pp. 597-604.
5. Opplinger, R.A., Bartok, C. (2012) ‘Hydration Testing of Athletes’, Sports Medicine, 32, pp. 959-971.
6. Borg, G. (1998) ‘Borg’s perceived exertion and pain scales’, Human Kinetics.
7. Skatrud-Mickelson, M., Benson, J., Hannon, J.C., Askew, E.W. (2011) ‘A comparison of subjective and objective measures of physical exertion’, Journal of Sports Sciences, 29(15), pp. 1635-1644.
8. Reed, J.L., Pipe, A.L. (2014) ‘The talk test: A useful tool for prescribing and monitoring exercise intensity’, Current Opinion in Cardiology, 29(5), pp. 475-480.
9. Helms, E.R., Cronin, J., Storey, A., Zourdos, M.C. (2016) ‘Applications of the Repetitions in Reserve-Based Rating of Perceived Exertion Scale for Resistance Training’, Strength and Conditioning Journal, 38(4), pp. 42-49.