Physiological response to injury and hot/cold

So, this post originally started off as a post to review the evidence behind contrast baths, however, I realised it would be best to explain the physiological effect of hot and cold on the body, and discuss healing times while I'm at it, due to the overlap.

So, here it goes, I will begin with healing times and process.

The healing process consists of 3 different phases, and these are:

1. Inflammation (0-48 hours)
2. Proliferation (5 days – 4 weeks)
3. Maturation (4 weeks – 2 years +)

Now, I've put the time frames up here as a guide. A popular misconception is that these time frames are distinct and seperate, as shown below:

When actually, each of these areas overlap, as one area is winding down, the next is building up it's response, as shown below:

Now, here I will discuss what each area does physiologically, in as brief and simplest way possible:

Inflammation

We are all familiar with this process. This is when the injured area, swells, become red in colour, with associated warmth, pain, and loss of function. In this stage, the initial bridging of collagen fibres begins.

The normal response in this stage is to apply the POLICE principles.

Now, I must point, at this stage, we all panic about swelling, and try our best to get rid of it. Swelling is a natural part of the healing process and we should let it take it's course, as the swelling is needed to get fresh nutrients to the area, and to remove cellular debris.

Chronic swelling, so swelling that is still present maybe a week after the injury is not necessarily good, as this will start to impact on the optimisation of the healing process, and this is where we would want to remove excess inflammation.

Swelling upon exercise of the injured area, at this stage, would still be normal.

Proliferation

This stage shows the signs of inflammation beginning to decrease, and pain levels decreasing too.

Collagen fibres are being laid down at the injured site at the peak rate at this stage and will progress to orientate themselves in line with imposed stresses.

Maturation

This stage should so no signs of inflammation and a huge decrease in pain, with pain only at end range. This stage should focus on restoring function and strength, and optimising collagen alignment.

Collagen fibre deposits peak around 3 months post injury, but will continue to lay down up to 2 years after an inujry (depending on the severity of the injury).

Maturation is more focussed on return to normal, with excess collagen fibres removal, optimisation of the collagen matrix to accommodate imposed stresses, and return to normality of the vascular supply.

This video discusses the three stages of healing in much more
detail, if that interests you, and you can stand the accent!

N.B. Pain is not synonymous with healing. Pain levels will decrease quicker than structural integrity of the injured site improves, so the risk of re-injury is still high, even if the pain has subsided.

This graph shows that after the injury, the pain levels drop
below the threshold quicker than the tendon recovery

It is also worth mentioning a few stats on the temperature of tissues.

Optimal tissue temperatures:
resting = 36.5ºC – 37.2ºC,
aim when exercising = 38ºC – 40ºC (as tendons exhibit plastic deformation at 39ºC, collagen at 40ºC)

Hot and Cold response

So, now I'll move onto the effect of hot and cold physiologically:

Hot and cold can increase or decrease symptoms of inflammation, and here's how:

Cold

Glenn ice climbing in cold conditions!
Copyright Glenn Manifold

Symptom	Response	How?	Additional info:
Pain	↓	Reduces nerve conduction velocity and increases the firing threshold	Considerations Rewarming after icing can take 3-4 hours With a muscle at 4cm depth from skin surface will have a 4ºC fall in 1hr Contraindications: Raynauds, Cold hypersensitivity, Open wound, Sensory defect, heart disease Precautions: Cardiac disease/hypertension, pelvis/groin area (bone marrow production/blood cells), left shoulder+neck area (proximity to heart)
Spasm	↓	Automatic protective response, prevents increase demand for O2
Metabolism	↓	Reduces need for O2 in surrounding tissue so less damage via hypoxia and reduces total debris. Less O2 means less secondary damage to other tissues
Blood flow	↓	Vasoconstriction of the blood vessels
Inflammation	↓
Oedema	↓	By vasoconstriction of blood vessels and increasing blood viscocity
Tissue extensibility	↓

Heat

The author bouldering in sunny,
warm Fountainebleau

Symptom	Response	How?	Additional info:
Pain	↓	By reducing the nerve conduction velocity and increasing the firing threshold	Precautions/contraindications: Diabetes mellitus Multiple sclerosis Peripheral vascular disease Spinal cord injuries Rheumatoid disease Possible side effects: skin burns
Spasm	↓	Automatic protective response, prevents increase demand for O2
Metabolism	↑	More energy to cells, increasing there productivity, plus increase in blood flow meaning more oxygen to area
Blood flow	↑	Vasodilation of the blood vessels
Inflammation	↑
Oedema	↑	By vasodilation of blood vessels and decreasing blood viscocity
Tissue extensibility	↑

I hope this post has given you a little more understanding around the healing process and the physiological effects of hot and cold, and hopefully this will aid understanding for future posts, such as the evidence behind contrast baths, that I'm currently working on.