(The original language of this article is French, and the graphs are shown from actual screenshots in the original language) Measurement Date: 24/09/2022
| Gender | Male |
| Age | 28 years |
| Height | 176 cm |
| Weight | 79 kg |
| Physical Activity | High – Sport: Cycling 6-10h/week |
Context: Exercise involves numerous transient physiological changes (increased heart rate, body temperature, etc.) creating stress for the body, necessary for physiological adaptations related to training¹². However, these physiological changes caused by exercise can lead to improper interpretation of body composition. Indeed, it has been shown that increases in skin temperature and blood flow lead to a decrease in measured resistances by 20 Ω³, which can result in incorrect body composition interpretations by algorithms. During this study, the values returned to baseline 1 hour after the exercise was performed; however, the exercise performed was moderate, and it is possible that a higher intensity exercise would result in more prolonged physiological changes.
In this case study, we will focus on the measurements obtained by the Biody XpertZM II after exercise and determine the point at which it becomes possible to obtain a reliable measurement to assess the effects of exercise on body composition, particularly on hydration status.
Here, a 28-year-old man, a recreational cyclist, performed a 1.5-hour exercise around the anaerobic threshold (AT, 75-80% of VO2max) on a home trainer with the following characteristics:
- 20 minutes 30 seconds of warm-up
- 6 blocks of 2 minutes 30 seconds (2 minutes at 85% AT; 30 seconds at 105% AT) with 2 minutes of recovery at 55% AT
- 4 minutes of active recovery from 55% to 25% of AT
The perceived intensity (RPE) was 9/10.
Four measurements were taken: before the exercise and three after the exercise at 30, 45 minutes, and 1 hour. During the exercise, the subject drank 750 mL of water containing a small amount of coarse table salt.
Subject Characteristics
Firstly, we can observe that the subject has a BMI slightly higher than the range associated with a normal BMI. The impedance ratio is low and the phase angle is relatively high, and these values are consistent with the subject’s training status.
If we look at the summary, we see that the subject has a higher muscle and bone mass than the reference value, which explains the BMI value. Hydration is normal despite being slightly lower than the reference value, but this is not problematic considering the water balance.
The indices confirm the previous observations regarding muscle mass, bone mass, and fat mass. The analysis of the indices shows that the muscle load and total load are adequate for the subject’s sporting practice.
Metabolism and Fat Mass
The basal metabolism is slightly higher than the calculated value, which can be explained by the higher muscle mass. The subject’s energy expenditure is at the higher end of normal energy expenditure, but considering 1) his level of physical activity and 2) the sport he practices, which is characterized by high energy expenditure during exercise, it remains consistent both for training days and for recovery.
In terms of fat mass, we can observe that it is slightly elevated, being at the higher end of the reference range. Considering the importance of the weight-to-power ratio in cycling, fat mass loss would be one of the first strategies to implement to improve this athlete’s performance.
Muscle Mass and Bone Mass
As observed in the summary, skeletal muscle mass, bone mass, and appendicular skeletal muscle mass are higher than the reference value. The difference from the reference could be considered small compared to some other athletes, but it remains consistent with the practice of an endurance sport, which requires 1) sufficient muscle mass to develop high power levels and 2) controlled muscle mass (thus hypertrophy) to allow for a weight-to-power ratio that facilitates maintaining a high power output during long-duration efforts.
Cellular Analysis
The cellular analysis shows a high total cell mass associated with good intracellular hydration. Additionally, it can be observed that this cell mass contains a significant amount of protein (+1.71 kg), which is consistent with the muscle masses observed previously.
Hydration
Firstly, if we look at total hydration, we can observe a slight deficit at the time of measurement; however, water balance is maintained with a small surplus of water at the extracellular level.
The slight deficit remains within the fat-free mass, but interestingly, we see that the water balance is completely different from the total water balance, with intracellular hydration being maintained.
Thus, despite the slight deficit, intracellular hydration is maintained within the fat-free mass, suggesting that the intra/extracellular imbalance observed in total hydration might be present within the fat mass.
Post-Exercise Analysis
Here, we will focus exclusively on total mass, total water mass, fat mass, fat-free mass, and water balance, which are the parameters most likely to be affected by acute exercise.
In the following figure, we can observe the changes in four of these parameters before and after exercise. It should be noted that beyond the 750 mL of water consumed during exercise, the subject did not drink or eat between the end of the exercise and the last measurement. We can observe that after the exercise, the subject loses 1.3-1.4 kg of body weight. The next question is to understand the causes of this weight loss.
At 30 minutes after the end of the exercise, two parameters decrease: total water (-0.93 L) and fat mass (-0.45 kg). Here, a first question arises: is the data interpretation correct 30 minutes after exercise? For water, we can say yes, considering the exercise performed. For fat mass, given that the exercise was aerobic, which uses lipids to produce the energy required for exercise, this decrease seems plausible. However, the degradation of one gram of lipids produces 9 kcal, so this would mean that 4050 kcal would have been consumed during this effort. Generally, it is considered that for this type of effort, the caloric consumption is around 1200-1500 kcal, and at these intensities, the majority of the energy consumed comes from carbohydrates. Thus, it seems unlikely that 450 g of lipids were consumed during the exercise. In conclusion, the measurement taken 30 minutes after exercise is not reliable.
At 45 minutes after the end of the exercise, we observe this time a loss of 550 mL of water and 1 kg of fat mass. Considering the water loss and the fact that the previous measurement was not reliable, this loss of 550 mL seems plausible. However, if we apply the same reasoning as before to the fat mass, this would mean that the subject consumed 9000 kcal in 1.5 hours, which is 1.5 times more than a professional cyclist during a stage of the Tour de France! Therefore, the measurement is also not reliable for observing changes induced by exercise.
Finally, 1 hour after stopping the exercise, we observe a water loss of 1.6 L and a gain of 200 grams of fat mass for a total weight loss of 1.4 kg and an unchanged fat-free dry mass. Given the observed figures, it seems that the measurement is accurate and that the obtained data can be used.
Returning to the physiology of exercise, three events occurring during this exercise can directly modify the obtained parameters: water loss through sweating, lipid consumption, which can decrease fat mass, and glycogen consumption, which would decrease fat-free dry mass.
Carbohydrate and lipid consumption during exercise can be estimated from the energy expenditure and the relative contribution of each of these two sources to energy production. We do not know the exact energy expenditure of this exercise, but according to the literature, we can estimate the subject’s caloric expenditure at 1500 kcal during this exercise. At this exercise intensity corresponding to approximately 75-80% of the maximum, we can also consider that we are close to the metabolic crossover point, which corresponds to the moment when 50% of the energy comes from carbohydrates and 50% comes from lipids.
Assuming this hypothesis for this case, 750 kcal would come from carbohydrates, and 750 kcal would come from lipids. At that point, 750/4 = 187.5 g of carbohydrates would have been consumed, and 750/9 = 83.3 g of lipids would have been consumed.
Therefore, the observed weight loss is related to water loss through sweating. The water loss is slightly overestimated, which is explained by the modification of the distribution of electrolytes (sodium, potassium) between the intra- and extracellular compartments. This slight overestimation is also responsible for the gain of 200 g of fat mass, given that the calculation of fat mass is Fat Mass = Total Mass – Fat-Free Mass.
When we look at the water balance, we can see that it is maintained 1 hour after exercise-induced dehydration in the case of our athlete. The water balance is maintained for this athlete, but this is not necessarily the case for all subjects, so it is a parameter to check after exercise.
Conclusion
This case study shows that it is possible to obtain reliable data with the Biody XpertZM II one hour after high-intensity exercise. It is not possible to determine changes in fat mass and/or muscle mass, but it allows for fairly accurate measurement of exercise-induced water loss and changes in water balance.
In this case, bioimpedance measurement is a relevant tool to advise individuals on their post-exercise rehydration and facilitate their recovery, as well as to develop optimized rehydration and recovery strategies in the context of monitoring high-level athletes. It can also allow for the monitoring of rehydration in these subjects following high-intensity training and/or competitions.
References
- Camera DM, Smiles WJ, Hawley JA. Exercise-induced skeletal muscle signaling pathways and human athletic performance. Free Radic Biol Med. sept 2016;98:131‑43.
- Lavie CJ, Arena R, Swift DL, Johannsen NM, Sui X, Lee DC, et al. Exercise and the cardiovascular system: clinical science and cardiovascular outcomes. Circ Res. 3 juill 2015;117(2):207‑19.
- Liang MT, Norris S. Effects of skin blood flow and temperature on bioelectric impedance after exercise. Med Sci Sports Exerc. nov 1993;25(11):1231‑9.
- Evans GH, James LJ, Shirreffs SM, Maughan RJ. Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. J Appl Physiol Bethesda Md 1985. 1 avr 2017;122(4):945‑51.
