Discussion
neurodegeneration
NEURODEGENERATION, CORTEX
Our study aimed to investigate the resistance training–induced alterations in brain metabolism of older adults in the hippocampus, primary sensorimotor cortex, and prefrontal cortex. We hypothesized that 12 weeks of resistance training would be associated with the increased relative concentration of tNAA and Glx, which may indicate increased neuronal density and enhanced glutamatergic neurotransmission in these particular brain regions. Although, there were no evident increases in tNAA and Glx after resistance training, relatively stable measures of tNAA/tCr and Glx/tCr were observed in the experimental group after 12 weeks. On the contrary, the control group experienced a significant decline in tNAA/tCr of SM1 and dlPFC cortices. Along with the reductions in tNAA/tCr, there was a similar decrease in Glx/tCr of the SM1 region in control group participants following 12 weeks. These results are in agreement with cross-sectional studies between young and old adults that have reported an age-associated decrease in NAA and Glx in the prefrontal as well as sensorimotor cortices [Interestingly, we observed a positive association of pre-to-post gains (∆) in peak torque of knee extension and flexion with ∆tNAA/tCr, ∆Glx/tCr (SM1 region) as well as with ∆Glx/tCr and ∆mIns/tCr (dlPFC region) of the experimental group. Previous literature has reported positive effects on the relative concentration of NAA levels in the hippocampus after 3 months of aerobic exercise [It is also important to discuss the potential factors that might explain the strength gain phenotype we observed, in response to resistance exercise within the experimental group. Previous studies have suggested factors such as nutritional habits, genetic variations including individual genetic polymorphisms such as in ACTN3 gene, and baseline characteristics that can justify the variability in response to exercise among individuals [Overall, based on our findings, it can be concluded that resistance training may be protective against aging-associated neurodegeneration and altered neurometabolism in primary sensorimotor and prefrontal cortices. The beneficial effect of resistance training is not only localized to the specific muscles being trained but in addition could concurrently lead to enhanced brain neuronal health. The older adults who underwent resistance training had a significant increase in their muscle strength and at the same time experienced to some extent an exercise-dependent increase in neurochemical markers of brain neuronal density and enhanced neurotransmission. Considering the exploratory nature of this study, the results should be considered keeping into account certain limitations. The sample size was small and was further reduced as a result of the sub-classification within the experimental group based on exercise response. Secondly, the exact order of exercises was not controlled and could potentially affect the strength gains among the participants. Finally, it should be noted that we did not perform tissue correction for 