Impact of Five Weeks of Strengthening Under Blood Flow Restriction (BFR) or Supplemental Oxygen Breathing (Normobaric Hyperoxia) on the Medial Gastrocnemius

Abstract

Background and Objectives: This study investigates the effects of a five-week training program on the medial gastrocnemius muscle, comparing two approaches: blood flow restriction (BFR) training and normobaric hyperoxia (oxygen supplementation). It evaluates three strengthening modalities (dynamic, isometric, and the 3/7 method) analyzing their impact on maximal voluntary contraction (MVC), muscle architecture, and perceived exertion. Methods: A total of 36 young healthy participants (21 females, 15 males) were randomized into six subgroups (n = 6 each) based on the type of contraction and oxygen condition. Training sessions (three per week) were conducted for five weeks at 30% of MVC. Measurements of MVC, muscle circumference, pennation angle, fascicle length, and perceived exertion were taken at baseline (T0), mid-protocol (T1), and post-protocol (T2). Results: All groups demonstrated significant increases in MVC after five weeks, with no notable differences between BFR and oxygen conditions. Structural changes were observed in specific subgroups: the BFR-isometric group showed increased calf circumference (p < 0.05), and the 3/7 groups exhibited significant fascicle length gains (p < 0.05). Perceived exertion was consistently higher in BFR groups compared to oxygen supplementation, particularly in dynamic exercises. Conclusions: Both BFR and oxygen supplementation are effective in enhancing strength with light loads, though they elicit different structural and perceptual responses. Oxygen supplementation may be more comfortable and less strenuous, offering a viable alternative for populations unable to tolerate BFR. Future research should focus on optimizing training parameters and exploring applications tailored to specific athletic or clinical contexts.

Keywords: 3/7 method; blood flow restriction (BFR); dynamic; force; human; hyperoxia; ischemia; isometric; medial gastrocnemius; oxygen; training; ultrasound.

Figure 1

System set up for the MVC test.

Figure 2

Ultrasound image showing the measures taken to fill in the formula for the fascicule total length: total (Lf) = lf1 + lf2 = lf1 + (h/sin μ). This approach is necessary since direct full measurement of fascicule length is out of the probe vision.

Figure 3

Audible Doppler device used to determine LOP.

Figure 4

On the left, O₂ concentrator and non-rebreather type oxygen mask; on the right, H-Cuff BFR model and pressure system.

Figure 5

Experimental protocol design. As indicated, all subjects were tested at the first session (S1) (T0), the seventh session (S7) (T1), and at the end of the protocol (fifteenth session—S15) (T2). %AOP, arterial obliteration pressure percentage; MVC, maximal voluntary contraction; Circumf, circumference; Penn angle, pennation angle.

Figure 6

Effect of the protocol on the fascicule length of the gastrocnemius medius in the different contraction groups after 3 weeks (T1) and at the end of the protocol (T2) in both oxygenation conditions. Results are expressed as mean ± SD. Statistically significant differences symbols: NS non-significant, * p < 0.05.

Figure 7

Effect of the protocol on contralateral leg MVC in the different contraction groups after 3 weeks (T1) and at the end of the protocol (T2) in both oxygenation conditions. Results are expressed as mean ± SD. Statistically significant differences symbols: NS non-significant, * p < 0.05, ** p < 0.01.