Figure 4: Weight of rats in research groups. Data were presented as mean ± SD. Ca: Citrus aurantium, CT: continued training, HIIT: high intensity interval training
Discussion
Findings of the present study showed that CT for two months significantly increased the aerobic power of elderly rats. However, CT and HIIT had no significant effect on the heart weight of elderly rats. Consistent with the findings of the present study, Azarian et al., (2019) reported that eight weeks of endurance training significantly increased the aerobic power of rats with Alzheimer's disease
(17), nevertheless regarding to ineffectiveness of HIIT on aerobic power, inconsistence with the findings of the present study, Constans et al,. (2020) reported that eight weeks of HIIT increased the aerobic power of rats (18). One of the reasons for the inconsistency of the reports of the Constans et al., (2020) with the present study is the type of subjects so that in the noted study used adult rats; however, the subjects of the present study were healthy rats. Consistent with the findings of the present study regarding the ineffectiveness of HIIT and CT on heart weight, Raufi et al., (2020) reported that eight weeks of resistance training had no significant effect on heart weight and left ventricular weight in obese rats
(8). The results of the present study also showed that HIIT for two months had no significant effect on adipose tissue weight and body weight of elderly rats. Contrary to the findings of the present study, Keikhosravi et al., (2020) reported that eight weeks of HIIT significantly decreased adipose tissue weight and body weight in elderly ovariectomized rats
(19). Exercise has been reported to be associated with increased aerobic power, physiological changes such as changes in heart rate, increased blood volume and hemoglobin, decreased blood pressure, blood distribution, and decreased lactic acid. Therefore, endurance training with this mechanism may increase aerobic power and increase lipolysis and ultimately lead to weight loss
(20). Many studies have shown that exercise is the best way to prevent and combat aging- induced sarcopenia by improving the physiological function of skeletal muscle tissue. Therefore, considering these positive physiological effects of exercise in the elderly, it seems that exercise can maintain or even increase muscle mass, increase muscle strength and ultimately reduce or prevent the prevalence of sarcopenia in these individuals. Also, regarding to the effect of exercise on cardiac hypertrophy, it has been reported that long-term exercises lead to cardiac hypertrophy through the mTOR/Akt pathway, so that moderate-intensity exercise is more effective than intense exercise
(21). Studies have shown that Akt1 is the major isoform in the regulation of exercise-induced physiological cardiac hypertrophy
(22). The mechanism of HIIT-induced cardiac hypertrophy, as with other exercises, has been shown to be dependent on the PI3K/Akt/mTOR signaling pathway.
In the present study, Ca administration for two months had no significant effect on aerobic power, heart weight, adipose mass weight and body weight of elderly rats. The antioxidant, anti-apoptotic and anti- inflammatory effects of Ca have been reported in various studies. In fact, Ca is used in the treatment of some diseases due to its compounds such as flavonoids, cyclooxygenases, synephrine, as well as its antioxidant effects
(23). Ca has been reported to contain bioflavonoids that play important roles in cell biology. Researchers have shown that the ingredients in this herb, such as synephrine and pectolinarigenin, are among the most effective antioxidant, anti-inflammatory and anti-cancer flavonoids. However, studies on the mechanism of action of Ca on aerobic power and body composition are very limited and have not yet been fully understood. Regarding the effects of Ca on the process of apoptosis, researchers believe that Ca by modulating autophagy and modulating the AMPK-mTOR signal pathway has good biological effects on the cell, and also inhibits cell death. In vivo and in vitro studies have also shown that citric acid and L-malic acid derived from fructose of this plant reduce caspase-3 levels
(24,25).
Regarding the interactive effects, the results of the present study showed that HIIT and CT simultaneously with Ca administration significantly increased aerobic power and heart weight; also HIIT along with Ca significantly reduced adipose tissue weight, nevertheless did not change body weight. Therefore, it seems that interval training along with Ca administration has a more favorable effect on increasing aerobic power and heart weight as well as reducing adipose tissue weight than either alone. Enabling to study the effects of different doses of Ca, measurement of calorie intake and calorie consumption in rats were the limitations of the present study; Therefore, it is suggested that in future studies, in addition to considering the limitations of the present study, the inflammatory and anti-inflammatory factors that are expressed in cardiac muscle tissue and adipose tissue be measured.
Conclusion
Regarding to results of present study, although CT can improve aerobic power in elderly rats, nevertheless it seems that CT and HIIT along with Ca administration can have more favorable effects on the body composition of elderly rats.
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