Should you apply heat when injured?

The answer is it depends. In the acute phase of any injury, it is typically best to avoid heat applications. During the therapeutic phase heat may be applied to help stimulate blood flow and relax tissues. If your injury causes immobilisation heat may help limit the loss of muscle mass and metabolic function.

nb - It is always best to seek professional guidance for your injury and circumstances.

These finding were presented in a paper called Daily heat treatment maintains mitochondrial function and attenuates atrophy in human skeletal muscle subject to immobilization in the Journal of Applied Physiology by Hafen et al in 2019.

When injury forces immobilisation there is commonly a detrimental impact of physical decline: metabolic health decreases and there is a loss in muscle function.

The objective of this study was to consider how heat treatment impacted the atrophy of metabolic and muscular state for subjects who were immobilised for 10 days.  

The research team took muscle biopsies and analysed MRIs of the vastus lateralis (a quad muscle) from 11 female and 12 male volunteers - who were all determined healthy – before and after 10 days of immobilisation.

Each subject had their left leg placed into a medical brace that fixed the knee at 60° flexion and were required to walk using crutches. This immobilised the leg in the brace, preventing its use and stimulating the natural muscle wastage through injury.

The participants were placed in counter balanced groups and either subject to a daily sham treatment (control) or a heat treatment for 2 hours.

The heat treatment increased intramuscular temperature by 4.2 +/- 0.29 with no temperature change in the control group. This was deemed comfortably by participants who scored the heat at 4 on a scale where 10 = extremely hot and 0 = no warmth.

As a consequence of the heat treatment, blood measures showed significantly elevated levels of heat shock protein (HSP) 70 and HSP90.

As a consequence of the immobilisation the respiratory capacity of coupled and uncoupled muscle fibres of the groups reduced by:

Decreases in the cross-sectional muscle area for the whole muscle were:

Deceases at the myofiber level were:

Considerations for athletes

Heat treatment may help to limit muscle loss and metabolic performance if immobilised through injury.

The research team highlight that their focus was the muscular response to heat therapy, and although they attribute the positive impact to heat shock, they cannot determine the extent to which other systems may have been influenced by the heating protocol. For example, a common response to heat is increased blood flow which brings nutrients. They observe that this warrants further consideration to explore the underlying mechanisms.