The Discrepancy Between External and Internal Load/Intensity during Blood Flow Restriction Exercise: Understanding Blood Flow Restriction Pressure as Modulating Factor

Abstract

Physical exercise induces acute psychophysiological responses leading to chronic adaptations when the exercise stimulus is applied repeatedly, at sufficient time periods, and with appropriate magnitude. To maximize long-term training adaptations, it is crucial to control and manipulate the external load and the resulting psychophysiological strain. Therefore, scientists have developed a theoretical framework that distinguishes between the physical work performed during exercise (i.e., external load/intensity) and indicators of the body's psychophysiological response (i.e., internal load/intensity). However, the application of blood flow restriction (BFR) during exercise with low external loads/intensities (e.g., ≤ 30% of the one-repetition-maximum, ≤ 50% of maximum oxygen uptake) can induce physiological and perceptual responses, which are commonly associated with high external loads/intensities. This current opinion aimed to emphasize the mismatch between external and internal load/intensity when BFR is applied during exercise. In this regard, there is evidence that BFR can be used to manipulate both external load/intensity (by reducing total work when exercise is performed to exhaustion) and internal load/intensity (by leading to higher physiological and perceptual responses compared to exercise performed with the same external load/intensity without BFR). Furthermore, it is proposed to consider BFR as an additional exercise determinant, given that the amount of BFR pressure can determine not only the internal but also external load/intensity. Finally, terminological recommendations for the use of the proposed terms in the scientific context and for practitioners are given, which should be considered when designing, reporting, discussing, and presenting BFR studies, exercise, and/or training programs.

Keywords: Effort perception; Metabolic stress; Muscle pain; Stimulus; Terminology; Vascular occlusion.

Fig. 1

Schematic illustration of the influence of blood flow restriction (BFR) on example parameters of internal and external load during several exercise modalities with (A) matched external load and (B) to exhaustion. The numbers on the individual parameters refer to the articles’ reference list

Fig. 2

Illustration of a conceptual framework of exercise with blood flow restriction. The external load is determined by a variety of exercise parameters, which also dictate the psychophysiological responses, and therefore, the internal load. The internal load in response to a specific external load depends on a multitude of influencing factors (i.e., environmental and personal factors). The level of relative cuff pressure, along with other variables, represents a modifiable environmental factor to manipulate the internal load. Relative cuff pressures between 40 and 80% of the individuals’ arterial occlusion pressure are assumed to induce favorable long-term adaptations