Sarcopenia, the progressive loss of muscle mass alone [1] or in combination with increased levels of adiposity, sarcopenic obesity [2], with aging, has gained a growing body of research. This decline in health is thought to be mediated by numerous mechanisms, including alpha‐motor neuron death, altered hormone concentrations, increased inflammation, and altered nutritional status [3], contributing to the prevalence of disease and increased mortality. Sarcopenia, has been associated with a greater risk of frailty, falls and disability [4], in addition to cardio-metabolic risks, and may induce obesity, increasing the risk of developing debilitating functional limitations [5,6]. This therefore, necessitates comprehensive and efficacious interventions that are also population specific.

Resistance training (RT) is one of the most consistently effective and safe approaches to combating sarcopenic obesity, by attenuating muscle loss, improving bone mineral density, lean muscle mass, ameliorating aerobic conditioning and strength and enhancing functional ability. RT at high intensity mechanical loads, specifically recommended at >70% 1 repetition maximum (RM) [7], tend to optimize beneficial adaptations. However, orthopedic issues and cardiovascular disease, often suffered by older adults, contraindicate RT of the affected joints and may exacerbate symptoms. Nonetheless, training below 65% 1RM seldom elicits increases in muscle size or strength [8]. Blood flow restiction training (BFRT) has been reported to elicit similar muscle cross-sectional area (CSA) and strength gains as traditional RT (>70% 1RM) in male [9-11] and female subjects [12] at lower intensities. BFRT involves the full occlusion of venous blood flow by applying a pneumatic cuff, band or strap proximal to the trained muscle, but allowing for free flow of arterial blood. At low intensities (LI) of 20-30% 1RM, studies have shown LI-BFRT to significantly improve hypertrophy [13], induce an approximately 3 times greater secretion of growth hormone (GH) compared to traditional RT (~70-80% 1RM) [14-16], and maintain improvements in strength after 3 weeks of detraining [17]. Additional benefits of LI-BFRT derive from its use of low mechanical loads allowing a shorter recovery time [18], minimal muscle damage [13] and therefore permitting a higher frequency of training.

In general, women participate in physical activity or exercise with depending various motivators and context preferences [19]. However, women would participate in irregular and less frequent participation than with physical barrier and time barrier [20]. Moreover, as Korean middleaged Women have marked gender differences in social support, motivating factors, and preferences for their participation [21], it cause vicious cycle to obtain health benefits by exercise. So it would be proper guidance for Korean middle-aged women to suggest safer, and less patient intervention is more effective preferable.

The current challenge for LI-BFRT is finding safe, tolerable and accessible methods of applying the restriction to a limb, without completely occluding arterial blood flow, and ensuring comfort and ease of use. The greatest variables between studies have been in the cuff size and pressure, used to induce an effective but safe level of restriction, minimize perceived exertion and pain, and optimize exercise volume. The vast range of cuff applications has produced numerous disparities within the research, leaving BFRT methodologies open to debate. Research is also sparse into LI-BFRT applied to the middle aged (aged 40+) and female populations. Thus, the current study will investigate the effects of LI-BFRT with low cuff pressures on body composition, lower limb muscular strength and power in middle aged women.

Participants mean age, height and weight were 47.35 ± 4.58 years, 159.96 ± 3.60 cm and 56.73 ± 4.83 kg, respectively <Table 2>. Blood pressure readings, prior to testing averaged 121.13 ± 10.51 mmHg and 75 ± 9.05 mmHg for systolic and diastolic pressures, respectively. There was no statistical difference between pre and post weight measurement values in all three groups.

This study provided support for the use of LI-BFRT, with intensities as low as 30% 1RM, to significantly improve muscle strength and power, and ASM/weight in middle-aged women. The present study used relatively low pressures of 100% and 120% of subjects’ bSBP (~157.3 mmHg). Such arbitrary methods have been criticized in previous literature as they do not account for individual limb size and may increase the risk of complete arterial occlusion [24]. However, further to the convenience of prescribing standardized pressures, Yokokawa et al [25] reported 120% bSBP as a safe and tolerable pressure to elicit significant physical fitness improvements in the elderly population, of whom we may predict, are at a higher risk of injury and complication than middle-aged women. In addition, as used in this study, one’s perception of intensity of exercise (i.e. cuff pressure) using LI-BFRT has been shown to be a good indicator of arterial restriction and suitability of exercise [13]. Despite the present study not reporting on pain levels, perception of intensity was deemed tolerable (ascertained pre-test), so much so that subjects were able to perform the assigned LI-BFRT exercise as required, without pain. It was thus demonstrated that safe pressures coupled with manageable intensities of exercise can elicit significant improvements in muscle strength, power and mass.

Cuff size is most likely a determining factor in the improvements of ASM/weight and strength with LI-BFRT in the present study <Table 3>. A study showed that when using the same protocol, an increase in elbow flexion strength was observed after training with a 7cm cuff, whereas a 12cm cuff induced no strength gains [9] (possibly as a result of complete arterial occlusion). 4cm, 5cm and 9cm width cuffs inflated to 160-240 mmHg have also been shown as effective combinations of pressure and cuff size for strength and hypertrophic gains following knee extension exercises [22]. However, none of these studies were completed using LI-BFRT on females, and all were carried out on subjects younger than 25 years [24]. Shaw and Murray [26] put forward that narrow cuffs may not induce a true restrictive pressure due to pressure loss with increasing limb tissue depth. Therefore, considering that women typically have smaller limb dimensions than men [27], the current study hypothesized that lower pressures would be adequate to induce a significant training effect. This was previously demonstrated by Takarada et al [15], when following a 16-week program of LI-BFRT at ~50-30% 1RM, using an 9cm cuff inflated to ~110 mmHg, significant increases in isokinetic strength and muscle cross-sectional area in middle aged women were observed. The present study not only used a narrower cuff (8cm), but also a shorter program duration (8 weeks) and lower exercise intensity (30%) yet increases in lower limb muscle strength and power were observed, and almost always greater or equal to RT <Table 4>. Hence, it may be deduced that the absolute pressure needed for muscular adaptation, with narrow to moderate cuffs in an aging female population, is much lower than previously demonstrated in men and women. Furthermore, the tolerability of LI-BFRT allows for untrained individuals to engage in exercise they may have typically avoided. Such benefits become pertinent when considering that physical discomfort is a common barrier in health behaviors of the aging Korean population [28].

To understand these adaptations, research suggests that increased cellular swelling may be a major mechanism [29], caused by the pooling of blood, an accumulation of intramuscular metabolites [30] and reactive hyperemia, ultimately stimulating various anabolic-signaling pathways [31, 32], resulting in a greater increase in growth factors [15], epinephrine [33] and norepinephrine [22, 15]. Accumulation of blood lactate concentration [34], significant elevations in post-exercise IGF-1 [34, 35] and the concomitant decrease in myostatin [36], have all been linked to the strength and mass improvements following LI-BFRT. However, it is important to note that there are disparities in the research regarding these mechanisms and their exact influences on the stimulation of physiological adaptations following LI-BFRT [37-39]. Significant improvements in mean power at 180°/sec Peak Tq were also observed in the present study <Table 4>, and greatest in the LI-BFRT group. This may be due to the concomitant increase in muscle strength, as was observed in this study, or the preferential recruitment of type II muscle fibers, via stimulation of group III and IV afferent fibers following reported changes in intramuscular venous pH [30], venous oxygen, carbon dioxide partial pressure and venous lactate concentration [33]. Furthermore, an indirect link between LI-BFRT and increased recruitment of type II muscle fibers was shown by an increased S6K1 phosphorylation, which occurs primarily in fast twitch muscle fibers, in the BFRT group following a “work matched” resistance exercise program [32]. Differences in protocol, particularly duration of effort, program length, exercise to failure [40], cuff size and pressure may account for the extent of physiological changes. Nonetheless, the inconsistencies in research indicate the likelihood of other mechanisms, beyond lactate accumulation and metabolic acidosis, playing a role in the adaptational responses to LI-BFRT. Limitations of the present study include the small sample size. The pre-test drop-out rate (average of 3 persons per group), due mainly to difficulties in performing the resistance training element of the program, meant sample size was small and may have affected statistical significance. Future studies may therefore want to address optimization of LI-BFRT by further investigating acute versus long term adaptations, intermittent versus continuous training and the potential changes to body fat percentage following LI-BFRT. The absence of significant change in body weight <Table 5> may be due to very slight reductions in lower limb body fat <Table 6, 7>, compensated for by increases in lower limb muscle mass, as demonstrated in the present study.

In alignment with prevailing BFRT research, our results demonstrate that improvements in muscle strength, power and muscle mass are achievable at a greater or tantamount degree to that of RT, though at a much lower intensity, indicating a direct effect of blood flow occlusion on muscle growth. Such an exercise approach may be a safe and efficacious preventative intervention in the case of sarcopenic obesity and its association with more severe health issues.

LI-BFRT lends itself well to home-based training programs and, for those to which high-load resistance exercise is a contraindication (e.g. arthritic or osteoporotic patients), a tolerable intervention. The middle-aged female population may find themselves without the time or energy to partake in RT, thus such low-impact activity appears more accessible and pragmatic.