Different types of endurance performance can be trained in specific ways. Adaptation of exercise plans should follow individual goals. Calculating the intensity of exercise the individual capabilities should be considered. Effective training starts within half the individual performance capability. Performance capability is expressed by
maximum heart rate. Best results can be achieved in the range between 55% and 65% of maximum heart rate. Aerobic, anaerobic and further thresholds are not to be mentioned within extensive endurance exercises. Training intensity is measured via the heart rate.
Endurance-trained effects are mediated by epigenetic mechanisms Between 2012 and 2019 at least 25 reports indicated a major role of
epigenetic mechanisms in skeletal muscle responses to exercise.
Gene expression in muscle is largely regulated, as in tissues generally, by
regulatory DNA sequences, especially
enhancers. Enhancers are non-coding sequences in the genome that activate the expression of distant target genes, by looping around and interacting with the
promoters of their target genes (see Figure "Regulation of transcription in mammals"). As reported by Williams
et al., the average distance in the loop between the connected enhancers and promoters of genes is 239,000 nucleotide bases.
Endurance exercise-induced long-term alteration of gene expression by histone acetylation or deacetylation with
histone tails set for transcriptional activation''' DNA in the nucleus generally consists of segments of 146
base pairs of DNA wrapped around
nucleosomes connected to adjacent nucleosomes by
linker DNA. Nucleosomes consist of four pairs of histone proteins in a tightly assembled core region plus up to 30% of each histone remaining in a loosely organized
polypeptide tail (only one tail of each pair is shown). The pairs of histones, H2A, H2B, H3 and H4, each have
lysines (K) in their tails, some of which are subject to post-translational modifications consisting, usually, of acetylations [Ac] and methylations {me}. The lysines (K) are designated with a number showing their position as, for instance, (K4), indicating lysine as the 4th amino acid from the amino (N) end of the tail in the histone protein. The particular acetylations [Ac] and methylations {Me} shown are those that occur on nucleosomes close to, or at, some DNA regions undergoing transcriptional activation of the DNA wrapped around the nucleosome. After exercise,
epigenetic alterations to
enhancers alter long-term
expression of hundreds of muscle genes. This includes genes producing proteins and other products secreted into the systemic circulation, many of which may act as endocrine messengers. In a study by Lindholm
et al., twenty-three 27-year-old, sedentary, male and female volunteers had
endurance training on only one leg during three months. The other leg was used as an untrained control leg. Skeletal muscle biopsies from the
vastus lateralis were taken both before training began and 24 hours after the last training session from each of the legs. The endurance-trained leg, compared to the untrained leg, had significant
DNA methylation changes at 4,919 sites across the genome. The sites of altered DNA methylation were predominantly in enhancers. Transcriptional analysis, using
RNA sequencing, identified 4,076 differentially expressed genes. The
transcriptionally upregulated genes were associated with enhancers that had a significant decrease in
DNA methylation, while transcriptionally downregulated genes were associated with enhancers that had increased DNA methylation. In this study, the differentially methylated positions in enhancers with increased methylation were mainly associated with genes involved in structural remodeling of the muscle and glucose metabolism. The differentially decreased methylated positions in enhancers were associated with genes functioning in inflammatory/immunological processes and transcriptional regulation. ==See also==