The effect of eccentric exercise on decompression strain

During high-altitude flight, extravehicular activity, and following diving, decompression sickness (DCS) can occur. Even mild symptoms of DCS (e.g., joint pain) may jeopardise a mission and necessitate treatment to resolve. The aetiology of DCS is thought to be the generation of gas bubbles within tissues and the vascular system, the latter known as venous gas emboli (VGE). These bubbles are believed to be formed from gas-saturated tissues and precursor bubbles, also known as micronuclei. There is limited knowledge regarding potential pre-decompression events that might provoke the development of DCS. Anecdotal observations made in reports suggest a relationship between strenuous exercise and musculoskeletal injury with an increased risk of DCS. However, no controlled studies in humans have been conducted to further explore this relationship. Given that aviators and divers frequently engage in strenuous physical activity, it is of interest, not least from a practical viewpoint, to determine whether and to what degree muscle damage induced by strenuous physical exercise may increase the risk of developing DCS. Eccentric contractions, where muscles lengthen under tension, cause greater exercise-induced muscle damage (EIMD) than concentric or isometric contractions. Although many eccentric exercises have been studied for their potential to cause EIMD, the effects of eccentric arm cycling remain unexplored.

In this thesis, we examined the effect of eccentric exercise on the formation of VGE as a marker of decompression strain. The thesis is based on four separate studies with the collective aim of investigating the effects of eccentric exercise on muscle damage and the formation of high-altitude-induced VGE.

The first study investigated eccentric arm cycling as a mode of exercise to induce muscle damage. The results show that 15 minutes of eccentric arm cycling is enough to induce EIMD, as evidenced by a reduction in isometric strength, delayed onset of muscle soreness, and elevation of markers indicative of muscle damage.

The second study investigated the effect of eccentric upper-body exercise on the formation of VGE. The study included two conditions: (i) eccentric exercise performed 24 hours prior to decompression and (ii) no exercise (Control). The results show that performing eccentric exercise 24 hours prior to a continuous exposure to 24, 000 feet for 90 minutes led to an earlier onset and increased VGE load compared to the Control.

The third study examined the effect of EIMD and its magnitude on high-altitude-induced VGE. The study included three conditions: (i) eccentric whole-body exercise, (ii) eccentric upper body exercise, and (iii) Control. The results show that the impact of eccentric exercise on high-altitude-induced VGE seems to vary depending on whether eccentric exercise has been performed in the upper body or lower body, rather than on the total muscle mass recruited.

The fourth study investigated the effect of eccentric exercise on muscle damage and inflammation and explored their possible roles in hypobaric VGE formation. The study included VGE-data from studies II and III, along with blood samples collected in conjunction with Control/exercise interventions and altitude exposures. The findings suggest that eccentric EIMD and inflammation are associated with a higher decompression strain. Furthermore, VGE load seems to induce and exacerbate systemic inflammation in a dose-dependent manner.

List of scientific papers

I. The effect of eccentric arm cycling on muscle damage and injury-related biomarkers. Gottschalk F, Gennser M, Eiken O, Elia A. Clinical Physiology and Functional Imaging. 2024 Oct; Online ahead of print. https://doi.org/10.1111/cpf.12911

II. Eccentric exercise 24 h prior to hypobaric decompression increases decompression strain. Gottschalk F, Eiken O, Elia A, Gennser M. European Journal of Applied Physiology. 2023 Sep; 123(9):2001-2011. https://doi.org/10.1007/s00421-023-05214-3

III. Eccentric exercise before a 90-min exposure at 24,000 ft increases decompression strain depending on body region but not total muscle mass recruited. Gottschalk F, Gennser M, Günther M, Eiken O, Elia A. Experimental Physiology. 2024 Sep;109(9):1517-1528. https://doi.org/10.1113/ep091853

IV. Eccentric exercise, muscle damage and inflammation in conjunction with high-altitude decompression. Gottschalk F, Gennser M, Günther M, Eiken O, Elia A. [Submitted]