**4. Transfer of maternal exercise induced effects on offspring and exercise modalities**

The effects of exercise, both acute and chronic, are partly mediated through the production and secretion of bioactive molecules termed cytokines. With exercise, an array of these metabolic factors are released by SkM influencing muscle metabolism as well as crosstalk between SkM and other organs. While extensive reviews have been published on this topic [93, 94], it is worth mentioning that these factors could mediate fetal programing as well. However, this is contingent on their placental blood barrier permeability. Many cytokines (i.e., IL-15, BAIBA, BDNF, Irisin, etc.) have an influence on energy metabolism and an overall positive effect on metabolic disease [93, 94]; however, the involvement of these cytokines in regulating offspring metabolic phenotypes is not yet understood. Recently, the effects of cytokine apelin have been shown to drive maternal exercise-induced metabolic reprogramming in offspring [19, 95]. Maternal exercise elevates apelin signaling which facilitates fetal muscle development and subsequently increases PGC-1α promoter demethylation, mitochondrial biogenesis and remodeling, and mitochondrial capacity [95]. This data suggests that maternal exercise-induced cytokine release could have a direct effect on fetal development by inducing specific adaptations that will later shape offspring metabolism. Accordingly, it is reasonable to postulate that different modes of exercise, based on their differences in cytokine expression profiles and differential metabolic demands [96–98], could have differing effects on offspring metabolic reprograming.

Exercise modes separate into aerobic and muscular strength training where activity is performed against a low resistance for a longer time or against high resistance for a short duration, respectively. These exercise modalities differ in the adaptations they elicit and are driven by the different energetic demands experienced during activity. During an acute bout of exercise, substrate oxidation is predominantly driven by the intensity and duration of exercise. There is a shift from predominantly fatty acid oxidation during prolonged low-moderate intensity exercise towards an almost exclusive reliance on glycolytic substrates during high-intensity exercise bouts. Aerobic training is often associated with improvements in cardiorespiratory fitness via an increase in maximal oxygen consumption and mitochondrial biogenesis. Specifically, aerobic exercise increases SkM mitochondrial protein synthesis, density, and oxidative function, which subsequently improves endurance capacity [99]. With this, it is not surprising that aerobic exercise results in a greater abundance of proteins involved in mitochondrial ATP production, TCA cycle, transport, and oxidation of fatty acids which are predominantly regulated through PGC-1α expression [99]. In contrast, while the effects of resistance exercise on these parameters are minimal, resistance training increases muscle size, strength, myofibrillar protein synthesis, and anaerobic capacity significantly more than aerobic exercise [99]. Both modalities improve glucose handling and are beneficial for improving glucose control predominantly through enhancing insulin sensitivity (i.e., greater GLUT4 expression) [99–101]. Additionally, aerobic training improves cardiovascular profiles and decreases adiposity, while resistance training seemingly has a very limited effect on either of these parameters [99]. Overall, while both modalities reduce the risk and lower the derangements of metabolic disease (i.e., obesity), the effects by which aerobic and resistance training influence metabolism vary to a great extent. With this in mind, it is reasonable to postulate that depending on the maternal exercise mode, effects on offspring metabolic reprograming will differ; however, research directly

#### *Influence of Maternal Exercise on Maternal and Offspring Metabolic Outcomes DOI: http://dx.doi.org/10.5772/intechopen.106566*

comparing the effects of maternal exercise modes on offspring metabolic health outcomes remains scarce especially with maternal muscular strength training.

While muscular strength training during pregnancy is safe and recommended, most research assessing the effects of prenatal exercise on offspring metabolic health utilizes aerobic only or a combination of aerobic and strength training. While these two exercise modes are beneficial for both maternal and offspring health, a delineation of their independent effects on offspring metabolic health is currently not possible [70]. Further, a comparison of the independent effects of maternal aerobic or strength training on offspring metabolism is primarily limited due to the lack of the studies utilizing maternal strength training [69]. To date, it is shown that a combination of aerobic and strength training during pregnancy increases cardiorespiratory fitness and muscle strength more so than aerobic or strength training alone [70]. Further, combined training has the most significant impact on decreasing gestational weight gain; however, more studies are needed to confirm these findings [70]. Evidence is similarly weak with inconsistent findings on the effects of combined training on improvements in birth weight; however, it is important to note that all exercise interventions increase the chance of the offspring having a normal birth weight and reduce the risk of macrosomia [70]. In conclusion, gestational exercise is safe and recommended considering the resulting array of positive metabolic changes in both mother and offspring.
