For fat loss to occur, we must induce a negative energy balance. Exercise itself helps to increase expenditure, while through nutrition we induce a caloric deficit by decreasing intake.
Does this mean that simply creating a caloric deficit is optimal for weight loss? Well, no, since the objective will never be to lose weight per se, but to lose fat and not muscle mass, and in this sense strength training plays a key role (among many other reasons that are not necessary to explain).
But speaking exclusively of fat oxidation, is strength training beneficial in this sense?
Recently this study was published (Allman et al 2019), where women with training experience were subjected to a strength training protocol to see if there was an increase in lipolysis of subcutaneous abdominal adipose tissue. What was seen? Well, strength training significantly increased lipolysis in abdominal subcutaneous adipose tissue, both during training and time after finishing it. But the most interesting thing is that not only was there lipolysis, but there was also an increase in fatty acid oxidation after the end of the training, corresponding to an increase in post-training resting metabolism, which we know as EPOC or in Spanish as ECOPE.
This also correlates with studies showing that women have greater lipid mobilization compared to men in strength training at the same relative intensity, probably due to greater stimulation of β-adrenergic receptors.
Importantly, although significant transient increases in lipolysis and fat oxidation with strength training were found in the study, it is unclear whether these acute elevations will result in long-term fat loss. Acute does not always reflect long-term improvement. direct improvement in long-term total fat mass.
Burrup et al 2017, concluded in their study that the more days, time and effort women of all ages devote to strength training, the lower their body fat and the greater their fat-free mass.
In fact, the authors emphasize that the more time spent weight training and the higher the intensity, the better a woman’s body composition.
They also stress the important effect of strength training in older women, where the adverse effects of menopause (insulin resistance, loss of bone mineral density and increased body fat) are reduced.
But if strength training is highly glycolytic, why is there a substantial increase in lipolysis and fat oxidation? First of all, knowing that the predominance of one or the other energy system does not inhibit the rest and secondly because we are talking about an effect during and after training, being substantial the oxidation of fatty acids when we are at rest after training. In other words, the glycolytic energy systems provide most of the energy required during intense strength training, which leads to a substantial decrease in muscle glycogen stores. Therefore, an increase in post-training fat oxidation provides a compensatory mechanism by which glycogen can be spared and thus be repleted post-training and fatty acids can be used as the main source of energy.
In conclusion, an acute strength training session can significantly affect localized fat mobilization and increased fat metabolism in strength-trained women. This is partly due to an increase in counter-regulatory hormones such as GH, epinephrine, etc. However, as I have discussed, the extent to which these events acutely contribute to chronic changes in body fat remains to be determined.