Table 2 A comprehensive definition of exercise fidelity

1. Frequency:

The proportion, number, or frequency of prescribed exercise sessions that the participant has attempted.

2. Intensity

The proportion or number of minutes spent at the prescribed level of exercise intensity. Intensity can be represented in different terms, including heart rate reserve (HRR), perceived effort (effort scales) and maximum oxygen consumption (VO₂ max). Intensity for resistance exercise may be expressed in terms of measured resistance or perceived effort (e.g., % of 1-rep max).

3. Quantity:

The amount of time that participants spent doing prescribed exercises, or other indicators of exercise quantity (e.g. distance walked, steps, lengths, repetitions, sets). Exercise quantity may be aggregated per session, per week or over other time periods. This should exclude (or be measured separately too) the warm-up and cool-down components of the exercise session.

4. Type/Quality of exercise (accuracy of movement):

Adherence of the participant to the specific types of exercise prescribed (e.g., walking, prescribed strength and balance exercises). For muscle-strengthening or functional exercises, this may also include the accuracy of body movements that the participant attempted to perform in relation to the body movements prescribed.

5. Safety:

Exercise safety may include several components. This includes:

a) Adherence to the warm-up and cool-down components during all exercise sessions.

b) Monitoring for any unwanted signs or symptoms (e.g. arrhythmia, chest pain) before, during, and after each exercise session.

c) Exercising above the prescribed intensity limit.

d) Movements that may be considered dangerous, or that put participants at risk (e.g., risk of falling).

6. Progression/Regression:

The participant’s progression (increasing the aerobic or muscular challenge presented by the prescribed exercise) or regression (decreasing the challenge) of the frequency, intensity, quantity or type of each exercise in line with the prescribed instructions. Progression or regression may be guided by assessment of perceived exertion, intensity, or functional ability [68, 69].

7. Appropriateness of progression/Regression:

The extent to which any progression or regression of exercise by the participant was commensurate with instructions for progression/regression provided by the practitioner, or the study protocol, or with general recommendations for exercise progression or regression. For example, ACSM recommends a gradual increase in frequency, intensity, time or type to prevent fatigue, injury or soreness of muscles and any risk at a longer period (17). Regression may be needed if the participant has had a setback in the progression of their fitness or physical functioning (e.g., a bout of illness or break from exercise).