THIS ARTICLE HAS BEEN RETRACTED MUSCLE VOLUME AND STRENGTH AND ARTERIAL COMPLIANCE AFTER WALK TRAINING WITH BLOOD FLOW REDUCTION IN ELDERLY WOMEN

To the Editor: Traditional high-intensity resistance training (HI-RT) is an effective tool to improve sarcopenia or osteoporosis, but previous research has indicated that HIRT reduces central arterial compliance, and the reduction may be associated with high rates of mortality in patients with end-stage renal failure and essential hypertension. Muscular blood flow restriction (BFR) during resistance training has been shown to elicit muscle hypertrophy similar to that during traditional HI-RT but with much lower training intensity. An intensity as low as that associated with walking, when combined with BFR, can lead to significant improvements in muscle size and strength, although the effect of low-intensity walk training with BFR on carotid arterial compliance has not been explored. Thus, the purpose of this study was to investigate the effects of BFR-walk training on carotid arterial compliance and muscle size and function in older people. Eighteen sedentary women aged 57 to 73 were divided into two walk training groupsFone with BFR (BFR-W, n 5 10) and one without (CON-W, n 5 8). The subjects in both groups performed 20 minutes treadmill walking at an exercise intensity of predetermined 45% of heart rate reserve (HRR) 4 days per week for 10 weeks. Age-predicted maximal heart rate (220–age) was used to determine HRR for each subject. Subjects in the BFR-W group wore elastic cuffs on the most proximal portion of both legs during training session (external compression: 200 mmHg). Magnetic resonance imaging–measured midthigh-muscle cross-sectional area (CSA) and maximum isokinetic knee extension and flexion strength (301/s) were measured before (pre) and after (post) training. Brachial blood pressure was measured using a semiautomated oscillometric device after subjects had rested in the supine position at least 15 minutes in quiet. Carotid arterial compliance was calculated according to the combination of ultrasound imaging and applanation of tonometrically obtained arterial pressure from the carotid artery. At the start of the experiment, there were no significant differences between BFR-Wand CON-W groups in terms of mean age (SE) (64 (1) and 68 (1), respectively), body mass index (22.8 (0.8) and 23.2 (1.0) kg/m), midthigh-muscle CSA, and knee extension and flexion strength. Resting blood pressure, heart rate, and carotid arterial compliance were also similar between the two groups. After 10 weeks of walk training, maximum isokinetic knee extension and flexion torques increased (P 5.004) in the BFR-W group but not in the CON-W group. Thigh muscle CSA also increased (P 5.001) in the BFR-W group but not in the CON-W group. Relative isokinetic strength per unit of muscle CSA increased in the BFR-W group, but there was no change in the CON-W group. Carotid arterial compliance improved (Po.05) in both groups, but the percentage change between the two groups was similar (Figure 1). There was no change in carotid and brachial blood pressure at rest for either group before and after the training. HI-RT is an effective tool for reversing sarcopenia and osteoporosis but has deleterious effects on central arterial compliance, but these results demonstrate that BFR walk training improves not only carotid arterial compliance, but also thigh muscle hypertrophy, which might be a useful method to improve muscle size and function and arterial compliance with a single type of training. A previous study found that the major contributor of resistance training– induced arterial stiffening is the elevation of blood pressure (250–320 mmHg) during each bout of HI-RT, although elevations of arterial blood pressure during moderate intensity aerobic exercise bout, as well as walking with BFR, are lower than during HI-RT. A study reported that total aortic elastin content was greater and calcium content of elastin was lower after aerobic exercise training in rats, which may contribute to the beneficial effects of BFR-walk training on arterial compliance. The findings of the current study also showed that significant hypertrophic response occurred in the thigh muscle only for the BFR-W group. This finding is consistent with previous investigations in young and older subjects. Another study demonstrated that a single bout of 20% of one-repetition maximum intensity knee extension exercise with BFR increased vastus lateralis muscle protein synthesis and the Akt/mammalian target of the rapamycin signaling pathway in young men. A low-intensity BFR exercise–induced increase in muscle protein synthesis was also confirmed in older men. These anabolic responses may contribute significantly to BFR walk training–induced muscle hypertrophy. In conclusion, walk training with BFR can produce thigh muscle hyper-