When our dogs strain a muscle, we often think that a couple of day’s rest is all that is required to heal and restore the muscle’s strength and function. A recent animal study tested this practice and the results may be surprising.

The animal study compared natural healing, massage therapy and exercise’s effect on muscle recovery from a contusion injury. The study measured a serum protein which is a marker of tissue injury along with changes in muscle structure.

The animal study involved 48 rats with induced muscle injury on the inner side of the right hind limb in the muscle belly of gastrocnemius muscle. The injury was caused by contact with the muscle causing a contusion.

Following the injury, the animals were divided into the following four study groups:

• Control group – natural healing

• Exercise and massage

• Massage only

• Exercise only

Exercise comprised the following:

• Uphill running on treadmill for 3 minutes with 10 degree incline at 12m/minute

• Downhill running on treadmill for 3 minutes with -10 degree at 14m/minute

Massage was performed on the injured leg, back and uninjured leg with moderate force for 4 minutes. Massage therapy commenced 48 hour post injury.

Both exercise and massage sessions occurred daily.

Fasting blood samples were gathered five (5) days prior to injury and then at intervals post-injury to 15 days.

Effects of natural healing, massage and exercise on serum CRP expression

C-reactive protein (CRP) is a biomarker for detection of acute and chronic infections. It is a protein that is detected during the acute phase: 6 – 12 hours of injury or infection. It is an indication of tissue injury or bacterial infection.

When tissue is injured or infected, inflammatory factors: neutrophils, monocytes and activated macrophages release Interleukin-1 (IL-1). IL-1 induces accelerated protein synthesis by hepatocytes and epithelial cells resulting in increased serum CRP expression.

An increase in CRP expression positively correlates with injury level and negatively correlates with recovery status.

The study found a significant increase in serum CRP expression (37 fold increase) from one day post injury compared with pre-injury levels. CRP expression peaked in day 2 post injury. From day 4 post injury CRP levels starting decreasing in all groups.

Serum CRP expression in each group were as follows:

Natural healing group

This group had the slowest recovery rate. For the first six days post injury there was no obvious change in the CRP levels. There was a moderate decrease in days 9 – 12. By the end of the study in day 15, CRP levels in the natural healing group were still higher than pre-injury levels.

Exercise and massage group

This group had the fastest decrease in CRP expression. By day 9, CRP levels were similar to pre-injury levels.

Massage only group

By day 12, CRP levels were similar to pre-injury levels.

Exercise only group

There was little change in levels in CRP serum levels in days 1 – 6. CRP levels starting to decrease by day 9 – 12 and by day 15 they had returned to pre-injury levels.

The study concluded that CRP increases positively correlate with injury levels. CRP decreases positively correlate with recovery levels. CRP could reflect healing conditions accurately as well as the final recovery status.

Effect of natural healing, massage and exercise on the structure of injured muscles

The study measured the structure of the injured muscle as they recovered and compared the effects of each rehabilitation method. The progression of skeletal muscle regeneration involves the following:

• Myofibre structure destroyed at the time of injury

• Myocytes atrophy and necrosis (cell death)

• Inflammatory cell infiltration

• Satellite cells activated

• Myoblast develop into myofibres

Changes in the muscle structure for each group in the study were as follows:

Natural healing group

Before the muscle injury, the myofibres were well organised and had even thickness.

In day 2 post-injury, the following were observed at the site of the injury:

• edema,

• part of myofibres disintegrated

• space between the myofibres disorganised

By day 5, the myofibres were filled with some connective tissue, poorly organised and had a tendency to necrosis. Day 8, filling among myfibres with connective tissue was obvious, the myofibres were atrophic, there was obvious necrosis, and area of degenerated myofibres increased. By day 12 and 16, the myofibres were still separated by large amount of cross linked connective tissue, there were atrophic, necrotic, and poorly organised.

Exercise and massage group

In day 2, post injury, the study observed partial myofibres were disintegrated, hyperemia among myofibres, and infiltrating inflammatory cells.
By day 5, neighbouring cells were adhering to each other and the broken myofibres were surrounded by connective tissue. At this stage of healing, the myofibres were poorly organised and there were some necrotic cells.

In day 8, myofibres began to align in order and tightly and there was little connective tissue between myofibres.

Finally by day 12 and 16, the myofibres were tightly aligned, there were no adhesions in the muscle, the nuclei of monocytes were displayed evenly, there were low levels of connective tissue, and histologically the muscle structure was complete and intact.

Massage only group

In day 2, hyperemia among myofibres was observed. The myofibres were disintegrated, poorly aligned and monocytes were necrotic.

By day 5, there was a large amount of connective tissue among myofibres and tissue hyperplasia. The myofibres were poorly organised. Infiltrating inflammatory cells were observed and there was little necrosis seen.

By day 8, myofibres were poorly organised and partially atrophic. There was decreasing inflammatory cells and connective tissue.

In day 12 and 16, myofibres were not adhering to each other. The myofibres were organised, the nuclei of monocytes were evenly displayed and histologically the muscle structure was complete and intact.

Exercise only

In day 2, the myofibres were broken and disintegrated, poorly organised, and there was a strong inflammatory response.

In day 5, the myofibres were disorganised, and myocytes were atrophic and necrotic.

In day 8, the ruptured myofibres were reconnected but still twisted, cross linked connective tissue was still present by the inflammatory response had been relieved.

By day 12 and 16, myocytes were full and well organised. Histologically the muscle structure was complete and intact.

How does massage therapy treat muscle injury?

Massage therapy has been widely used to treat injured skeletal muscle and aid muscle recovery. Muscle injury treated with massage indicates that massage can activate regeneration of injured myofibres. The mechanisms by which massage causes these effects could include the following:

• Blocking pain signals

• Improving blood and lymphatic perfusion

• Suppressing local inflammation

• Signalling pathways induced in skeletal myofibres in a particular direction by physical traction of massage

• Regulating protein synthesis, glucose uptake and immune intervention

• Influencing regeneration of muscle stem cells

In this study, the massage groups showed a return to pre-injury serum CRP levels by the end of the study period. It is thought that massage therapy regulates serum CRP expression by suppressing inflammation. In this study, neutrophils accumulated at the injury site after one hour from injury and remained at the site of the injury for five days.

In the massage only group, there was a large concentration of neutrophils and higher proliferation rate leading to activation of monocytes and release of IL-1. Neutrophils release a series of proteolytic enzymes to

• degrade disrupted extracellular matrix,

• activate blood coagulation

• promote macrophages to target injured myofibres and tissue gaps to remove cell debris and algogenic substances in serum

• improve microenvironment of injured tissues

• suppress overexpression of inflammatory factor CRP thereby suppressing local inflammation

It is thought that the pressure of massage releases inflammatory lymphokines from the liver. As such massage has a critical role in macrophage engulfment and activating satellite cells. In the massage only group in this study, satellite cells appeared 24 hours post injury and started dividing and proliferating leading to collagen secretion.

Massage also played a significant role in the restoration of muscle structure. The force from massage pushed fibrillary tissues toward well aligned arrays in the direction of existing muscle fibres despite being filled by a few connective tissues.

Further, massage decreases adhesion of muscle to skin and surrounding muscles and suppressed hyperplasia of connective tissue, and monocyte atrophy and necrosis. By suppressing connective tissue proliferation, the massage groups showed decreased scarring compared to other groups. The possible mechanism for this is new vessel vascularisation at the site of injured tissues. Increasing circulation around injured muscles leads to accelerated removal of dead cells, congestion, and edema among injured tissues.

How does exercise treat muscle injury?

One week post-injury, the exercise only group showed a rapid decrease in CRP expression at the end of the inflammatory phase and beginning of the recovery phase. Additionally, at this stage, satellite cell activation and development of myoblasts to myofibres was observed.

By day 12, CRP expression had returned to pre-injury levels. It is thought that exercises’ role in muscle recovery is associated with specific forms of exercise. In this study, uphill running required concentric muscle contractions of the injured tissue which could have a role in protecting the muscle from further tears. Concentric contractions cause the muscle terminals to move to the centre of the muscle. This protects injured myofibres and allows cell membranes to regenerate and reconstruct thereby suppressing CRP expression.

On the other hand, downhill running requires eccentric muscle contractions of the injured muscles. Eccentric contractions push the muscle terminals to the origin and insertion of the muscle potentially leaving the injured tissues in the muscle belly exposed to re-injury. Eccentric muscle contractions in the early stage of muscle injury could result in the following:

• Collagen degeneration and recurring damage to the cell membrane.

• New vessel vascularisation at the injured location being hindered thus delaying infiltration of neutrophils, macrophages and other blood derived cells necessary for healing. Circulation at the injury site is also necessary for the development of myoblasts to myofibres to restore the muscle structure.

While some forms of exercise may be detrimental to muscle recovery, the exercise only group in this study showed that exercise had a positive effect on restoring motor functions in the injured muscles.

Takeaway message for dog owners

The induced muscle injury in this study was a contusion caused by contact to the muscle. Our dogs can easily damage muscles in this way by contacting the ground (slip and fall), contacting with an object (sport equipment like jumps or tunnels, furniture, or walls in the case of a slip) or another dog during play. The findings in terms of CRP expression and changes in muscle structure during the recovery process can therefore be applied to muscle injury in dogs.

In this study, the combination of exercise and massage had better effects on inflammatory removal, skeletal muscle regeneration, skeletal muscle fibrosis control, and muscle tissue reconstruction than natural healing or exercise or massage alone.

While exercise had better effects on restoring muscle strength and balance, the study indicated that performing eccentric muscle contractions of the injured muscle during the acute phase of an injury may cause recurrence of injury. It is therefore recommended for eccentric contractions to be introduced one week post injury.

Full Stride provides remedial massage treatments for dogs recovering from muscle injury and with chronic musculoskeletal conditions.

Until next time, enjoy your dogs.

Sources:

Lyu, P., Chen, X., & Liu, Q. (2019). Effect of Exercise and Massage Therapy on Injured Muscular Structure and C-Reactive Protein Expression. Pakistan Journal of Zoology, 51(5), 1621-1621.

Image by dife88 from Pixabay