Dynamometers are commonly used in the health field to measure the strength of a muscle or a group of muscles and to assess its progress. Dynamometers are found in functional rehabilitation centers and physiotherapy practices as well as with occupational therapists, high-level athletes and even in the fitness room.

The dynamometer is a medical instrument that is mainly used in functional rehabilitation (physiotherapy) or in sports medicine, but it can also be used in ergonomics or occupational medicine. It is used to assess muscle strength measured through stress tests.

Different forces, corresponding to the solicitation of different muscles, can be evaluated:

• tractive force ;
• flexion ;
• gripping;
• compression.

Composition

There are two types of dynamometers:

• mechanical dynamometers which take direct measurements evaluated by means of a spring;
• digital dynamometers (or digital) which use electronics to measure a voltage and transcribe it on the screen.

Force measurements are given in Newtons (kg.m / s2), kilograms or pounds.

Data interpretation can be done by programs or applications, with automatic data transfer in the case of digital dynamometers.

A medical dynamometer measures the muscle force applied by the user on the instrument.

In what contexts do you use a dynamometer?

• In physiotherapy, as part of functional rehabilitation to assess the progression of muscle recovery following trauma or surgery;
• in medicine, to detect muscular dystrophy of genetic origin, linked to aging, malnutrition or invasive treatment;
• in a sporting context (especially high level) to evaluate the muscular performances and the functional capacities of the athlete, and to adapt the training sessions according to the needs;
• in ergonomics to adapt a workstation or check its conformity;
• in occupational medicine.

Public concerned or at risk

Dynamometers used in a therapeutic context are mainly used in the context of rehabilitation of a limb or of the hand following a tendon injury, a nerve injury or neuromuscular disorders.

In rehabilitation centers, there are isokinetic dynamometers, which offer a very wide range of functions allowing very complex rehabilitation.

Hand dynamometers

Collin’s dynamometer

It measures muscle pressure and traction. The measurement is carried out up to 70 kg in steps of 50 g. It consists of a stainless steel ring placed around a dial equipped with a slider. To measure the pressure, the hand firmly encloses the ring, which causes the cursor to move towards the maximum pressure reached.

To measure the traction, it suffices to pull on a chain previously attached to the instrument, which moves the cursor to its maximum position.

The handle dynamometer

It is equipped with a handle that the patient must tighten as strongly as possible to measure the closing force of his hand. In certain models, the position or the resistance of the handle can be modified, thus requiring a greater or lesser muscular contraction effort, which makes this instrument accessible to children and the elderly as well as to adults. The measurement can range up to 100 kilograms.

The most advanced accurately report strength, muscle fatigue and recovery time. The result can be read on an analog or digital dial. Some analog models have two hands, one of them remaining fixed on the maximum value reached during the exercise. Numerical models can offer different valuation calculations.

Traction dynamometers

They allow you to test the force exerted in real time during a precise movement. The digital versions make it possible to determine the maximum force reached, the time required to reach it and its holding time. Software makes it possible to record and store data in order to make comparisons and measure the evolution and progression of rehabilitation, for example.

Isokinetic dynamometers

These relatively complex dynamometers allow mobilization (passive or active) of a limb or its muscle strengthening. The working speed can be programmed, by adapting the resistance of the instrument to the force exerted by the subject. They are used for pathologies of the shoulder, knee, ankle, back, but also within the framework of the rehabilitation of neurological or cardiovascular pathologies in rehabilitation centers.

Manual muscle testers, or dynamometer brakes

They are used to assess the breaking force of a muscle or a group of muscles. The examiner applies the anvil of the dynamometer to the limb to be tested. The limb is kept in a stable position favorable to resistance against the force exerted. The examiner presses harder and harder on the limb, until the subject can no longer resist and gives in. The force to which the subject has yielded is called the breaking force.

Use determines the choice of dynamometer. The dynamometers on the market are small and easily transportable instruments. Some are delivered with carrying cases and different functional kits depending on the type of force to be measured: pushing, pulling, squeezing, resisting, etc.

The models used must bear the CE mark to comply with the regulations.

The different models

Mechanical dynamometers

Collin’s dynamometer and mechanical handle dynamometers sell for between $ 100 and $ 200.

Digital dynamometers

Electronic models run on batteries or rechargeable batteries, with an autonomy of up to 70 hours.

The most sophisticated make it possible to instantly calculate the force, the average force, the maximum or minimum force, to establish statistics, etc. and can be linked to interpretation and data management software, with data transfer by USB or Bluetooth.

It usually takes several hundred euros to acquire a digital dynamometer offering good performance.

Dynamometers in industry

The use of dynamometers is very widespread in fields other than medical: automotive, aeronautic, mechanical, railway, food, textile, etc. industries.