Muscular strength is defined, according to Stone (1993), as the ability to exert a force on an object or against an external resistance. The question of the evaluation of muscle function, and in particular the evaluation and quantification of this force, remains an enigma in our daily practice as physiotherapists.
Although, even if the evaluation tools are not lacking, they are not always reliable, oftentimes they are difficult to carry out or inefficient. Unless you are properly equipped.
However, we know that the precise evaluation of the force is essential. An improvement in muscular capacities leads to better performance and a reduction in the number of injuries in athletes.
It allows better functional efficiency, better efficiency in activities of daily living (ADL) and also prevents musculoskeletal disorders (MSDs), micro traumatic pathologies (arthropathy, tendinopathy, osteoporosis) and more broadly in one’s overall health.
Finally, in the elderly, it significantly reduces the risk of falling and improves the quality of life by avoiding deconditioning, thus offering the guarantee of functional longevity. Finally, physical activity in general improves neurogenesis and promotes a better cognitive state, thus preventing Alzheimer-type dementia.
In addition, the precise quantification of muscle strength makes it possible to define precise rehabilitation or training objectives, to measure progress over a period of time. This is in order to give “feedback” and maintain a goal that can be achieved for patients, which helps them stay motivated.
When looking at the literature, the tools used for strength assessment are mainly the “international testing”, the Medical Research Council scale (Vilella, physiotutors), the “break-test” associated or not with a scale, the calculation of 1RM, the functional tests and the dynamometer.
This article will go through a simple evaluation of each of these tests to help you figure out the ones that are more suitable for your subjects.
1. The Medical Research Council Scale (MRC)
As its name suggests, the MRC allows a scoring from 1 to 5, and not a quantitative assessment of muscle strength. Its analysis is not very precise in the isolation and evaluation of a muscle alone.
Furthermore, if we want to follow the method proposed by Williams (1956) and Lacôte (1982), we must place the patient in such a way as to recruit the muscle in the most optimal way, by controlling the compensations made by the synergistic muscles, and ask him for a contraction against the manual resistance of the evaluator, which he will rate from 0 to 5 according to the following grid:
0: No evidence of contraction
1: Presence of a minimal contraction, no movement without gravity
2: Full range of motion without gravity
3: Full range of motion against gravity
4: Full range of movement against gravity, with partial resistance or notion of fatigue
5: Full range of movement against gravity with normal resistance (normal muscle)
This rating can be refined by adding plus (+) or minus (-) signs as well. We understand the subjective side of this evaluation, in particular from rating 4 (“partial resistance” and “notion of fatigue”) and more particularly the difficulty of its realisation (“by observing and controlling the compensations”).
In addition, there are other limitations to this rating, such as the high variability of results and inter-country reliability. We must also include an absence of standard or reference value per muscle and a muscular evaluation that is neither very functional nor analytical in nature.
2. The Break-Test
The break-test is a subjective assessment tool that determines the strength of a muscle or muscle group by applying resistance that gradually increases (Conable, 2011). It is a possible alternative to other techniques for measuring muscle strength but remains possible only if the strength of the evaluator is greater than that of the patient for the muscle or muscle group tested (Stratford, 1994).
The gradual increase in the examiner’s resistance is not quantifiable, unless a dynamometer is added, and does not make it possible to obtain an accurate value. It is possible to use a scale to quantify the difference in force in a very relative way using the weight of the examiner before and after resistance is applied to the subject, but this technique is terribly unreliable.
3. THE 1RM Test
The 1RM test is “the maximum weight that can be lifted once, while maintaining correct lifting technique” (Kraemer WJ). The 1RM test has good to excellent test-retest reliability according to professionals, regardless of technical experience, functional exercise, muscle evaluation and gender or age of the participants (Grgic, 2020).
However, the intraclass correlation coefficient (ICC) varies according to the studies from 0.64 (48) to 0.99 (26). In addition, the protocol for carrying out the test is not standardised.
This is specifically seen during the warm-up prior to the test, which can generate fatigue depending on its duration (1 to 10 repetitions or 5 minutes of cycling) and its intensity (40 to 80% theoretical 1RM), on the number of trials (3 to 8 trials) and on the recovery time between each trial (1 to 5 minutes).
Typically the recommended recovery time after a maximum effort is, usually between 5 and 7 minutes (22). So even if this evaluation method may appear to be reliable, it is conceivable that a vagueness still exists on its practical realisation, mostly on the reliability of its results obtained and therefore on the relevance of its use (17-18).
4. Functional Tests
As the name suggests, functional tests are of great use when it comes to evaluating functional movement. However, their effectiveness remains limited for measuring the strength of a muscle or a muscle group, or even a muscle chain, functional or not.
They bring into play a set of muscles in a very global way and do not make it possible to determine which muscle is deficient in the movement.
We only measure overall performance. Observing the compensations is often very difficult, even when asking the subject to perform the movement at a very slow speed. The intensity or the load developed is proportional to the weight of the body but cannot be precisely quantified and the exercises required require expertise and technical accuracy.
Finally, we measure an effort of resistance, or even endurance and not strength. This is because the duration of each test is 60 seconds, with rest periods of 10 seconds, i.e. approximately 4 and a half minutes of continuous exercise, which corresponds to a recruitment of the aerobic sector and not to the anaerobic alactic sector mainly solicited in the efforts of force.
In the end, they will be of no use in accurately or reliably assessing the strength or resistance of a muscle or of a muscle group. However, they will prove to be a judicious complement if we want to measure the effectiveness of these muscles when performing complex functional, sporting or professional movements.
The validity and reliability of the Muscular Fitness Test (MFT) comprising a sequence of 4 functional exercises performed for 60 seconds and interspersed with a 10-second break was measured using 489 participants (Huerta Ojeda, 2020).
The 4 exercises performed are, in order, “sit-ups”, “push-ups”, “deep squats” and “burpees”. The measurements taken are the heart rate at the end of the test, the percentage of resting heart rate and the quantification of the effort felt or Rating of Perceived Exertion (RPE).
This test appears to be valid and reliable for measuring strength and resistance to effort in healthy young adults (p<0.01).
5. The Dynamometer
The dynamometer is the “gold standard”, when it comes to carrying out a precise quantification of the strength of a muscle or a muscle group of a subject, in the purpose of setting up a specific reinforcement program. It also makes it possible to precisely objectify progress after the implementation of a protocol.
Most mechanical dynamometers are fairly easy to use. They make it possible to give a reliable value of the force (Newtons, Kilograms or pounds) which is exerted on them whether measuring traction or compression.
KINVENT’s hand-held dynamometer K-Push is lightweight and versatile, and has been designed to meet the need for modularity for a quick assessment on-the-go. It allows you to assess the maximum and isometric strength of almost 40 muscular groups with its range of accessories.
Apart from K-Push, other KINVENT tools enable accurate assessment and easy extraction of data in a digital format, accessible on a tablet or smartphone, allowing for easier and faster data transmission.
This allows a clinician to visualise the progress of his patient. It also gives the patient precise and quantified objectives to achieve, and to appreciate in a concrete way their progress, or their regression.
To learn more about KINVENT’s physio solutions and packages, visit our page at bmec.asia/kinvent
- KINVENT | physio.kinvent.com/article/going-from-qualitative-to-quantitative-physiotherapy-muscle-assessments/
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