You are walking with your dog when Fido bounds off at full speed. Seconds later, he returns holding one leg off the ground. What do you do? Ice, rest, visit to the vet or nothing.

What effect does the partial loss of function in one leg have on the dog’s body?

Muscle is a plastic tissue. It adapts to various tasks and can respond to changing functional demands. When functional requirements change, then muscles can immediately respond by changing their patterns of recruitment and activation. That is, the areas of the muscles that are “recruited” is adaptable as is the muscle groups that are activated to fulfil a task. Over time, changes to functional demands in recruitment and activation patterns can change gene expression, namely changes in tissue growth and re-modelling to reflect the changed functional requirements.

However, when a dog is injured and loses partial function in a limb, their muscles need to adapt quickly. This typically results in an immediate change in muscle recruitment. In this case, the animal will adopt compensatory strategies in response to the partial loss of limb function. These compensatory strategies may involve one or more of the following:

• Locomotor adaptation which is seen through changes in the animal’s gait.

• Change in muscle activity.

• Redistribution of body weight.

• Dynamic shift of the position of the centre of mass to alter the load on the trunk and limbs. This shift of centre of mass is achieved by changes in muscle activity.

Study of changes in muscle activity in dogs

A study investigated the changes in muscle activity in dogs with induced hindlimb lameness. The study was designed to evaluate the following:

• The onset and offset of muscle activity including the timing of peak activity.

• The maximum activity and location of the activity within the muscle (relative to the location of the device used to gather data.)

The study recorded the activity of three muscles while dogs trotted on a treadmill. The following three muscles were measured:

• Triceps brachii – Forelimb muscle that extends the elbow.

• Vastus lateralis – Hindlimb muscle that extends the stifle.

• Longissimus dorsi – Back/ trunk muscle that stabilises and mobilises the dog’s trunk when they are in motion. They provide a firm foundation for the generation of hindlimb forces by stabilising the pelvis and controlling the forces transmitted through the trunk.

The study involved eight dogs that are acclimated to trotting on a treadmill. Muscle activity measurements of the three muscles were taken prior to and after inducing lameness in a hind limb. Lameness was induced by taping a small sphere to the paw of each dog.

What effect does a hind leg limp have on dog’s muscles?

Triceps brachii

In both the normal and lame state, there were two main phases of muscle activity. The first phase was during the late swing phase to the late stance phase and the second before lift-off through to the first half of the stance phase.

During the trotting gait, the long and lateral muscle heads are active prior to touch down and remain active until the mid-stance phase. This muscle activity is eccentric and controls passive flexion of the elbow joint from gravitational forces. Subsequent muscle activity involves concentric contraction to extend the elbow joint and provide propulsion in the stance phase.

The change in muscle activity and the timing of the activity was insignificant in either forelimb in the lame state. Likewise, only minor changes in vertical forces and gait changes were observed in the lame state.

Vastus lateralis

The activity of this muscle starts in the last quarter of the swing phase through 40% of the stride cycle.

In the lame condition, activity in the affected limb decreases significantly. The muscle activity decreased 15% in the “injured” limb and increased by 43% in the contralateral limb. These findings show the injured limb bears significantly less body weight. In a chronic condition this would likely result in loss of muscle mass in the quadriceps group of muscles.

Recruitment patterns and timings also changed following the “injury”. Peak activity in the contralateral limb occurred later and there was no change in the timing in the affected limb.
In both hind legs, the duration of muscle activity increased. In the affected limb, it increased by 6% and 23% in the contralateral limb.

The changes in muscle activity and timings in the contralateral limb after lameness indicates a significant weight shift to the contralateral limb. The dog’s gait is also affected with increased duration in the stance phase following a partial loss of function of a hindlimb. Increases in muscle activity in the contralateral limb increased in the second half of the stance phase when concentric contraction extends the stifle to exert propulsive forces in the hind limb. The increased muscle activity is due to a pronounced stifle extension for forward propulsion to compensate for the loss of power in the lame limb.

Longissimus dorsi

This muscle has two phases of activity. The first is during the second half of the stance phase and the second during the second phase of the swing phase. The bilateral activity of this muscle serves to stablise the trunk against vertical forces of the hind limb.

In the lame condition, a change in muscle activity timing was noted. The first burst of activity started later and peaked later on the contralateral muscle. The peak of the second burst of activity was smaller on the contralateral muscle. The increase in activity in the contralateral muscle is consistent with long axis rotation to the sound side of the dog’s body. Additionally, other animal studies have shown an increase in activity in the gluteaus medius which would also be expected in this study. This activity increase is due to changes in limb trajectory in the lame state namely, skewing limbs to move the sound limb under the centre of mass.

Unilateral changes in muscle activity is associated with stabilising the pelvis in response to changes in the hind limb motions.

How do dogs compensate when they limp?

While this induced lameness model only measured the muscle activity of three muscles, it shows the compensatory strategies that dogs adopt to maintain movement. Similar changes in muscle recruitment and timings would occur in muscles throughout the dog’s limbs, trunk, and neck.

The current model induced a distal limb injury in the paw. It has been shown that there are differences in muscle recruitment and timings depending on the source of the lameness i.e. stifle or hip. Regardless, muscle activity changes to compensate for loss of limb function.

Further, the current model illustrates muscle activity adaptation in response to acute, short term injury. Chronic conditions would result in differences in muscle recruitment and timing patterns. Long term changes in muscle activity would trigger changes in tissue responses and result in muscle remodelling. Additionally, muscle forces determine joint loading, so long term changes in muscle activity may also bring about skeletal remodelling or joint degeneration. Finally, changes in muscle forces over joints can affect the stability of joints which in turn can change the trajectory of limbs and cause weight shifts to unload limbs.

Based on the impact of even a short term injury, treating muscle injury or soreness in dogs is important to avoid long term muscle remodelling.

How to treat muscle strain in dogs?

When a dog incurs a soft tissue (muscle, tendon, connective tissue) injury, please treat immediately. For more information please see http://www.fullstride.com.au/blog/dog-is-limping for more details.

After the acute phase of injury has passed (72 hours since the injury), then massage, passive range of motion, stretching and remedial exercise will aid the soft tissue healing process and restore normal function to the limb. For more information please see https://www.fullstride.com.au/blog/how-can-myofunctional-therapy-help-dogs-with-a-soft-tissue-injury

Full Stride works with dog owners who want to proactively maintain their dog’s musculoskeletal health. Treatments are available in the dog’s home (Brisbane’s northern suburbs) and from my treatment room on Brisbane’s north side.

Until next time, enjoy your dogs.

Source:

Fischer S, Nolte I, Schilling N. Adaptations in muscle activity to induced, short-term hindlimb lameness in trotting dogs. PLoS One. 2013;8(11):e80987. Published 2013 Nov 13. doi:10.1371/journal.pone.0080987