Resistance Training and the Role of Heat Shock Proteins

Our body continuously fights to find a balanced state where we can expend just enough energy to complete tasks, but not too much, so that we waste energy needlessly.

The human organism has an astounding ability to respond to anything that challenges its own survival – be it physiological or psychological – with rapid success. Through a process referred to as homeostasis the body is able to preserve its internal milieu based on how it adapts to the external environment.

In order to achieve homeostatic balance, a number of regulatory pathways, mediators and messengers must co-function to find, and then maintain such balance. One of those regulators are heat shock proteins.


What are heat shock proteins and what do they do?

Heat shock proteins (HSPs) exist within the cells of all living organisms. They make up a large family of proteins that aid in protein synthesis and protect each cell from a variety of protein damaging stressors. They function to adapt to unfavourable conditions. For that reason they are also often referred to as ‘stress proteins’.

Cells respond to protein damaging stressors by initiating a response termed the “heat shock” or “stress” response, which involves the rapid and transient increase in a specific set of proteins. [1]

These specialized proteins are categorized into families, or ‘subsets’ such as HSP60 and HSP70. These terms are based on
molecular weight. They are named ‘heat shock’ proteins due to them being isolated during research on hyperthermia, and whilst internal heat within the body can trigger them, it may not necessarily be what entrains their production.

During times of minimal stress, HSPs help to signal immune cells that fight off disease. However, for the purpose of this article we are more interested in what happens during times of physiological stress, as it helps us understand the response to resistance training and their role in muscle adaptation.

HSPs facilitate protein transport, repair cellular damage within the muscle and replace protein where needed, and also help to attract amino acids in order to encourage them to convert into muscle fibres. Heat shock proteins also assist in maintaining and restoring correct protein folding – basically they protect newly formed proteins, make sure they assemble properly and don’t form incorrectly [2].

HSPs essentially maintain order by ‘babysitting’ other proteins and keeping them focused on their own jobs – you can see why they are referred to as ‘chaperones’ due to their role in assembling and regulating multi-protein complexes and cell cycle control.

Key Point: Heat shock proteins are specialized protein cells that aid in protein synthesis and protect from unfavourable situations such as cellular damage.

HSP70


Resistance training and heat shock proteins

Not only are HSPs present in eukaryotic and prokaryotic cells, they are also present in striated muscle – and when we place a sufficiently overloading stress on the muscle such as with weight training, HSPs will elevate to meet the imposed demands placed upon it.

As such, they are considered to assist in adaptation to exercise in skeletal muscle that may subsequently protect muscles against stressors [3].

Heat shock proteins can be used as markers of muscle damage, much like creatine kinase is. The overload needed to induce an increase in these proteins can be achieved in a number of ways – however different types of exercise elicit different HSP responses. As with creatine kinase, there is potential for these proteins to be used to assess whether an athlete is excessively fatigued, overreaching and overtraining.

Lower intensity endurance exercise has been found to release HSP60, which plays a key role in the translocation of proteins and cytoprotection due to its location [4], whereas higher intensity exercise (as with resistance training) releases HSP70.

What The Studies Say

In humans, eccentric training has been found to significantly elevate the HSP70 family of heat shock proteins. For example, one study using 11 healthy males [5] showed that repeated maximal eccentric contractions of the quadriceps muscles induced HSP release from the 30-minute post-exercise period, and was still elevated 4 days later. Levels of HSPs increased to ~15 fold resting level. The authors of the study reported that HSP70 seems to be involved in recovery and the remodelling/adaptation processes in skeletal muscles. 

Likewise, the same response was seen in a study by Thompson et al [6] after only a single bout of eccentric training in the biceps brachii muscle of male and female volunteers. In this study, HSP70 was found to increase by 234% at the 48 hour post-intervention point. 

Unsurprisingly, it has been proposed that HSPs play an important role in the hypertrophy response to resistance exercise too. In another study, again by Thompson et al [7], it was suggested that heat shock proteins, alongside mitogen-activated protein kinase (MAPK) responses, were important to long-term skeletal muscle adaptations including the hypertrophy adaptation.

Key Point: Resistance exercise has been shown to increase HSP70, particularly in the presence of maximal eccentric loading.

Heat-Shock-Proteins-DNA


Muscle growth and heat shock proteins

As we’ve seen from the research so far, HSPs are affected greatly by exercise, particularly resistance training. Ultimately, HSPs are part of a self-repair system that is initiated practically straight after exercise, and continues until the restoration process is complete. These proteins are associated with the signalling response to muscular overload, and as such can be thought of as part of the trigger to muscle repair and regeneration. 

Although skeletal muscle is comprised of many proteins, the dominant ones – actin and myosin, exist within the functional sarcomere in an organised and repetitive manner designed to overcome tasks. When these functional units are placed under mechanical or metabolic damage during resistance training, damage will invariably occur, and in order to minimize undesirable side effects in the form of protein degradation, organisms such as HSPs have developed as an evolutionary conserved protection mechanism [8].

HSPs appear to assist other signalling pathways in regulating the repair and growth of skeletal muscle tissue when catabolic activity has been triggered and has reached its peak — this makes HSPs a key protein in preserving muscle and initiating new muscle tissue. They are a powerful tool in your muscle building and protein synthesis arsenal. Essentially, HSP70 is a critical skeletal muscle protein that positively regulates muscle size [9].


Summary

Heat shock proteins specialized protein cells that increase in unfavourable situations such as in high heat or during exercise, to assist in maintaining skeletal muscle homeostasis. They function to facilitate protein transport, repair cellular damage within the muscle and replace protein where needed, and help to attract amino acids in order to encourage them to convert into muscle fibers.

Due to their presence in striated muscle, exercise has been demonstrated to increase circulating HSPs – particular resistance exercise where there are elements of maximal eccentric loading. As such, HSPs elevate to meet the imposed demands placed upon the muscle, and subsequently promote an adaptation to exercise in skeletal muscle that may protect muscles against the stressors of mechanical and metabolic stressors.

Unsurprisingly, HSPs have been proposed to be one mechanism that may explain hypertrophy signalling, with one of their roles being to regulate the repair and growth of skeletal muscle tissue when catabolic activity has been triggered, and has reached its peak.


References

  1. Frier, BC & Locke, M. Heat stress inhibits skeletal muscle hypertrophy. Cell Stress Chaperones. 2007; 12(2): 132-141
  2. Li, Z & Srivastava, P. Heat-shock proteins. Curr Protoc Imunol. 2004; Appendix 1: Appendix 1T
  3. Huey, KA et al. Heat Shock Proteins, Exercise, and AgingIn: Asea, AA & Pedersen, BK. Heat Shock Proteins and Whole Body Physiology. Springer Netherlands, pp387-400
  4. Barone, R et al. HSP60 is muscle fiber-type specific and increases after endurance training: mice model. IJAE. 2013; 118(2) (Supplement): 20
  5. Paulsen, G et al. Maximal eccentric exercise induces a rapid accumulation of small heat shock proteins on myofibrils and a delayed HSP70 response in humans. Am J Physiol. 2007; 293(2): R844-R858
  6. Thompson, HS et al. A single bout of eccentric exercise increases HSP27 and HSC/HSP70 in human skeletal muscle. Acta Physiol Scand. 2001; 171 (2): 187-93.
  7. Thompson, HS et al. Exercise-induced HSP27, HSP70 and MAPK responses in human skeletal muscle. Acta Physiol Scand. 2003; 178(1): 61-72
  8. Dubińska-Magiera, M et al. Contribution of small heat shock proteins to muscle development and function. FEBS Letters. 2014; 588(4): 517–50
  9. Senf, S. Skeletal muscle heat shock protein 70: diverse functions and therapeutic potential for wasting disorders. Front Physiol. 2013; 4: 330

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