Muscle fiber cross-sectional area is increased after two weeks of twice daily KAATSU-resistance training

The purpose of this study was to examine the effect of low-intensity (20% of 1-RM) resistance training (LIT) combined with restriction of muscular venous blood flow (KAATSU) on muscle fiber size using a biopsy sample. Three young men performed LIT-KAATSU (restriction pressure 160-240 mmHg), and two young men performed LIT alone. Training was conducted twice daily for 2 weeks using 3 sets of two dynamic lower body exercises. Quadriceps muscle CSA was measured by magnetic resonance imaging at midpoint of the thigh. Muscle biopsies were obtained from the vastus lateralis (VL) muscle using a needle biopsy. Mean relative change in 1-RM squat strength was 14% in the LIT-KAATSU and 9% in the LIT after two weeks of the training. Mean changes in quadriceps muscle CSA was 7.8% for LIT-KAATSU and 1.8% for LIT. Changes in muscle fiber CSA was 5.9% for type-I and 27.6% (p<0.05) for type-II in the LIT-KAATSU, and -2.1% and 0.5%, respectively, in the LIT. Mean fiber CSA changed 17.0% in the LIT-KAATSU, but not in LIT (-0.4%). We concluded that skeletal muscle and fiber hypertrophy, especially type-II fiber, occur after high frequency KAATSU training.