This single-case study examined an arterio-venous shunt patient (20 year old male) where a main artery supplying the left leg in the deeper anterior pelvis was connected to a returning vein, possibly due to previous trauma received while playing high level Team Handball. Due to this A-V shunt muscle blood flow was transiently restricted in the left leg when the patient was exercising with his lower limbs (verified by ultrasonography imaging), which led to marked onset of muscle fatigue within 1-2 minutes of running activity. This pathological condition had evolved over a few years of continued sports activity, resulting in visible hypertrophy of his left leg.

AIM: To study the effect of chronic blood-flow restricted (BFR) exercise conditions on skeletal muscle size and myogenic satellite cell (SC) expression in an arterio-venous shunt patient.

METHODS: Muscle biopsies were obtained from the left (L; affected limb) and right (R) VL muscle, and examined for mean fiber area, quiescent (Pax7+) and activated SCs (MyoD+, Myogenin+, Ki67+) and myonuclei number using immuno-fluorescence techniques.

RESULTS: Mean myofiber area was 38% greater in L vs. R (6729 ± 2382 vs 4898 ± 2050 µm2), while myonuclear content was 14% higher (4.2 ± 1.6 vs 3.7 ±1.3 myonuclei per myofiber), myonuclear domain was 22% larger (1807.0 ± 912.9 vs. 1483.9 ± 765.5 µm2 per myonuclei) and Pax7+ cells were 93% more abundant (0.189 ± 0.43 vs. 0.098 ± 0.297 Pax7+ cells per myofiber) in L compared to R. In addition, marked up regulation in MyoD+ (+266%), Myogenin+ (+31%) and Ki67+ (0.022 vs. 0.000 SCs per myofiber) positive SCs was observed in L vs R.

DISCUSSION: Using between-limb comparisons the present single-case study demonstrate that chronic exercise-induced BFR due to arterio-venous shunting led to a marked up-regulation in myogenic satellite cell activity within all stages of the cell cycle, which was accompanied by substantial muscle hypertrophy. Specifically, muscle fiber cross-sectional area (40%) and myonuclei number (15%) were elevated in the affected leg, together with an elevated myonuclear domain (20%). This single-case study confirms previous result from our Lab demonstrating that blood-flow restricted muscle exercise leads to a marked activation of myogenic SCs, upregulated myonuclei number and marked myofiber hypertrophy.