Objective muscle mass assessment in dogs: thigh circumference measurement

A dog's muscle mass plays a significant role in its health and physical abilities. To ensure proper monitoring of strength and detect any muscular abnormalities, objective assessment of muscle mass is crucial, particularly if you are a physiotherapist or rehab therapist. While various methods are available, the most prevalent way to measure muscle mass in dogs is through the thigh circumference using a tape measure. Physiotherapists and rehabilitation therapists often take note of this measurement to establish a baseline before implementing a strength and conditioning program. They will then re-evaluate the measurement at a later date to determine if there are satisfactory improvements in muscle mass and strength.

Tape measure: for measuring muscle mass in dogs

How reliable is this measurement and what factors can influence the readings between people and between repeat measurements?

One key aspect of any measurement technique is its reliability. Intra-reliability refers to the consistency of measurements taken by the same observer on different occasions.  A study by Bascuñán et all (2005) evaluated the factors influencing thigh circumference measurement in dogs and concluded that there was a 'low fidelity outcome measure with a large inter- and intra-observer variability.'  Another study by Smith et al 2015 looked at the inter and intratester reliability of anthropometric assessment of limb circumference in labrador retrievers and concluded that only the antebrachial measurement was reliable and that a single measurement was as reliable as using the mean of triplicate measurements. 
With these findings, it's easy to ask the question - What is going wrong with the measurement techniques? What factors do we need to take into account so that the recordings are more reliable? 

Factors that need to be taken into consideration to minimise the variability of recordings

Positioning of the dog

When measuring muscle mass, the positioning of the dog is really important. To get a consistent reading it is preferred to have the dog in lateral recumbency where they are most relaxed.  Try and keep the position of the limb in the same position for each recording, for example, I take my thigh measurements with the dogs' hip in neutral each time to maintain consistency.  Taking measurements in standing can pose a few more issues such as the dog having the ability to have varying degrees of weight-bearing capacity each time you measure (which may skew results,)  placement of paw/limb and movement of the dog. 

Fur length/ coat

Often before surgery, the limb is clipped back of fur which poses a bit of a problem by the time the dog is ready for physio/rehab and to have measurements taken.  To get a true evaluation of changes over time, consistency is key, so either the limb needs to keep having the fur clipped back for each measurement or a measurement pre-surgery/pre-clipping is needed. 

Positioning of the tape

To get a true indication of limb muscle mass it makes sense to place the tape over the 'meatiest part' of the limb where most of the muscle bulk lies. But how do we find this point exactly and how do we ensure that we repeat this measurement consistently to avoid variability?  In my practice at least, I am the only one measuring thigh circumference so my landmarks are always consistent. For the thigh, I try and measure the mid portion of the thigh and use, as guidance, the midpoint between the great trochanter of the femur and the lateral epicondyle. 

With varying degrees of intra-tester reliability found in research and the many factors that can influence this, I still think that thigh circumference measurements for objectively assessing muscle mass in dogs has its place in the rehabilitation clinic.  Until there are advancements in methods for practically assessing muscle growth,  physiotherapists and rehab therapists need to consider the variables influencing these readings and try and maintain consistency within these which will ultimately lead to more  accurate recordings.

References:
Bascuñán, A. L., Kieves, N., Goh, C., Hart, J., Regier, P., Rao, S., Foster, S., Palmer, R., & Duerr, F. M. (2016, May 5). Evaluation of Factors Influencing Thigh Circumference Measurement in Dogs. Journal Name, 1st published, 2016-05-05

Smith, T. J., Baltzer, W. I., Jelinski, S. E., & Salinardi, B. J. (2015). Inter- and Intratester Reliability of Anthropometric Assessment of Limb Circumference in Labrador Retrievers. Journal Name, 1st published, 08 October 2015