Blood Starvation of Muscles During Training

muscle fiber fasicle

Blood flow restriction to muscles during training was shown by a recent study to induce changes in the muscle that increased contractile function. These changes were observed at the cellular and biochemical level.

 

An exciting field of research right now is how the muscles act when blood flow is constricted. A recent study showed that constricting blood flow during training increased muscle fiber cross sectional area, muscle stem cells and nuclei in the muscle (myonuclei).

The study (Jakob Nielsen, et al. 2012.  Proliferation of myogenic stem cells in human skeletal muscle in response to low-load resistance training with blood flow restriction) assigned twenty healthy males to perform 23 knee extension training bouts for a period of 19 days. Ten subjects performed the training with a pneumatic cuff placed on their thigh to limit blood flow (blood flow restriction or BFR). The other ten subjects served as a control and had no blood flow restriction. Muscle biopsies were taken pre-training, 8 days into the training intervention, 3 days post-training intervention and 10 days post-training intervention.

Interestingly, the subjects who had their blood flow restricted retained an increase in strength 5 days and 10 days post training intervention. The control subjects’ strength returned to pre-intervention levels 10 days post-training intervention. The cause of this sustained strength increase in the experimental group can be explained at the cellular and biochemical level.

Subjects who had their blood flow restricted saw increases in muscle stem cells, muscle nuclei, and muscle fiber cross sectional area. The differences were measured by muscle type as well.  Type I fibers are slow twitch fibers, responsible for aerobic work. Type II fibers are fast twitch and provide anaerobic work. Both mucle fiber types saw a large increase in Pax7+ expressing stem cells in subjects who had blood flow constricted. As the figure below shows, both muscle fiber types saw an increase in myonuclei when the subject had blood flow to the muscle constricted (blood flow restriction or BFR). The BFR change in type II muscle is surprising given the low intensity (normally aerobic) exercise. No change in either muscle fiber type was seen post-training in the control group (CON).

The muscle fiber cross-sectional area increased in both groups of subjects during training. However, the control group lost virtually all gains post-training. The blood flow restriction group maintained gains in muscle fiber cross sectional area 3 and 10 days post training. The authors suggest that hypoxia-induced protein synthesis is responsible for the gains seen in muscle fiber cross-sectional area in the blood flow restricted muscles.

In conclusion, blood flow restriction during training appeared to strengthen muscle function even after the cessation of the training program. The muscle achieved an increase in contractile power through increases in muscle fiber cross-sectional area, muscle stem cells, and myonuclei.  The discussed results have clinical significance: blood flow restriction may help patients regain lost or damaged muscle.

However, blood flow restriction likely does not extend beyond potential clinical applications to elite training programs.  Both groups followed the same training sequence. It would be reasonable to believe that training performance would be hurt by blood flow restriction. Thus, for a healthy, elite athlete doing high-intensity training, blood flow restriction would hamper their ability in a workout.