A study led by UK researchers has shown for the first time that human muscles possess a 'memory' of earlier growth, or hypertrophy.
Muscle cells are able to 'remember' which genes are activated or inactivated during physical exercise and use this information to grow larger later in life. This finding could have important implications for athletes training and recovering from exercise-related injuries, or those cheating with performance-enhancing muscle-building drugs.
In the study, published in Scientific Reports, eight healthy males completed a programme of 21 weeks alternating acute and resistance training with a period of no exercise. The investigators performed a biopsy pre- and post-exercise and isolated the genetic material from the muscle fibres. They used a genome-wide approach to screen over 850,000 regions of the human DNA that carry special chemical tags known as epigenetic modifications. Usually, a gene marked with such an epigenetic tag is not expressed.
'In this study, we've demonstrated the genes in muscle become more untagged with this epigenetic information when it grows following exercise in earlier life. Importantly, these genes remain untagged even when we lose muscle again, but this untagging helps "switch" the gene on to a greater extent and is associated with greater muscle growth in response to exercise in later life - demonstrating an epigenetic memory of earlier life muscle growth!' said Dr Adam Sharples, a senior study author at Keele University in Stoke-on-Trent.
The group of DNA regions untagged during the entire training plan contains genes belonging to a cellular signalling system - PI3K/AKT pathway – critical for cell proliferation and protein synthesis. The scientists hypothesised that the enhanced epigenetic untagging of these genes would lead to increased muscle protein levels and hypertrophy.
Robert Seaborne, study co-author and PhD student at Keele University, hopes that the identification of the epigenetic memory involved in muscle bulk increase could help define more appropriate sporting regulations. 'If an elite athlete takes performance-enhancing drugs to put on muscle bulk, their muscle may retain a memory of this prior muscle growth. If the athlete is caught and given a ban - it may be the case that short bans are not adequate, as they may continue to be at an advantage over their competitors because they have taken drugs earlier in life, despite not taking drugs anymore,' he said. 'More research using drugs to build muscle, rather than exercise used in the present study, is required to confirm this.'