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Despite the many health benefits of resistance training, it has been suggested that high-intensity resistance exercise is associated with acute increases in intraocular pressure which is a significant risk factor for the development of glaucomatous optic nerve damage. Therefore, resistance training using a variety of forms (e.g., resistance bands, free weights, weight machines, and bodyweight) may be harmful to patients with or at risk of glaucoma. An appropriate solution for such people may involve the combination of resistance training and blood flow restriction (BFR). During the last decade, the BFR (a.k.a. occlusion or KAATSU training) method has drawn great interest among health and sports professionals because of the possibility for individuals to improve various areas of fitness and performance at lower exercise intensities.
- glaucoma
- occlusion
- ocular health
1. Introduction
Glaucoma poses a serious and increasing problem for public health as it is the leading cause of irreversible blindness and significant reductions in quality of life [1]. Glaucoma is a group of progressive optic neuropathies characterized by a degeneration of retinal ganglion cells and retinal nerve fiber layers that result in changes in the optical nerve head, leading to visual field loss and eventual blindness [2]. Risk factors include age and frailty, gender, myopia, genetics, family history, smoking, race, systemic hypotension and hypertension, vasospasm, use of systemic or topical steroids, migraine, obstructive sleep apnea syndrome, and most significantly, increased intraocular pressure (IOP) [3]. Although the primary strategy for managing glaucoma is based on pharmacological or surgical interventions, other factors such as diet, exercise, or sleeping position should also be considered to reduce the progression of this disease and avoid symptoms (e.g., visual field loss) [2]. Therefore, physical activity needs to be carefully and individually prescribed to induce positive instead of adverse effects on ocular physiology depending on the type of exercise and participants’ characteristics.
A primary exercise intervention for muscle and strength development is resistance training [4]. Regular resistance training provides several benefits for the human body such as improving body composition, glycemic control, cardiovascular health, increasing bone mineral density, facilitating physical functions, and enhancing mental health [5]. Therefore, this type of physical activity is readily practiced by populations of all ages and is recommended as a part of the World Health Organization 2020 guidelines [6]. This also applies to the elderly, who can effectively counteract or reverse the aging process with resistance training [7]. This type of training can be accomplished using bodyweight, resistance bands, free weights, or weight machines. Resistance bands and bodyweight training may provide an alternative when traditional weight equipment is unavailable. However, determining the appropriate training intensity and maintaining progression over time, as well as achieving high involvement of particular lower body muscles are more challenging with these forms [8]. Therefore, free weight and weight machine training should be prioritized and for optimal benefits, the American College of Sports Medicine (ACSM) recommends 1−3 sets per exercise of 8−12 repetitions with 70−85% of one repetition maximum (1RM) for novice and 3−6 sets of 1−12 repetitions with 70−100% 1RM for advanced trainees [9]. However, for many populations, the above-mentioned training demands while recovering from injuries or undergoing rehabilitation and dealing with different forms of chronic inflammation and pain (e.g., arthritis) may make adherence to this recommendation challenging. Moreover, it may be potentially harmful to glaucoma patients, especially given that people over 60 years of age are at an increased risk of glaucoma and have to counteract the progressive loss of muscle mass and strength with age [10].
Even though resistance training offers a variety of positive health effects, it has been hypothesized that high-intensity resistance training may cause acute increases in IOP [11,12,13,14], which is a substantial risk factor for the onset of glaucomatous optic nerve injury [15]. Therefore, resistance training following ACSM guidelines may be harmful to patients with or at risk of glaucoma. According to the available data, increases in IOP after high-intensity resistance training vary on the exercise and load applied, with heavier loads and exercises involving several muscle groups showing the greatest alterations [14,16,17]. This phenomenon may be related to core stability or bracing during high-intensity exercise that is achieved by trunk muscle contraction and often results in a Valsalva maneuver [18]. Consequently, the increases in intra-abdominal and intrathoracic pressures are transmitted to systemic vascular and intracranial transmural pressures [19], affecting IOP. In addition, body positioning during exercise also influences IOP levels, with greater IOP values in supine than sitting or standing [20]. This creates significant limitations in terms of designing and progressing resistance training programs, especially in at-risk patients beginning a resistance training program. However, it is also worth noting that the IOP response is reduced in trained individuals, indicating that fitness levels may modulate this phenomenon [13]. Hence, this may be related to several adaptive processes which accompany regular resistance training, highlighting the importance of considering training status to prevent/reduce undesirable effects on ocular health and gradual progression models recommended by the ACSM.
Considering the above, an appropriate solution for glaucoma patients or those at risk of glaucoma may involve the combination of resistance training and blood flow restriction (BFR). This training solution involves the use of an inflatable cuff, tourniquet, or elastic wraps that exert high pressure at the proximal part of the limb (lower or upper), to reduce arterial blood flow and to occlude venous blood flow during physical exercise. Resistance training loads with BFR exercise are reduced due to increased metabolic stress [21], cell swelling [22], intramuscular signaling [23], and enhanced endocrine system responses from the reduction of arterial inflow to the exercising limb [24]. Hence, while maintaining similar effectiveness to high-intensity resistance training in terms of muscle mass and strength [25], an adjunctive benefit of BFR exercise may be a potential reduction of IOP secondary to reduced training loads (20–30% 1RM).
3. Safety Concerns and Blood Flow Restriction Resistance Training
The BFR method has been used to an increased extent for different purposes. Commonly cited approaches include increasing rehabilitation potential [26], improving athletic performance [27,28], and improving general health [29]. Therefore, different groups of individuals and a wide array of BFR protocols have been examined [30,31,32,33]. However, most of these studies have enrolled healthy participants with a focus on physical performance outcomes and body composition change [23,34,35] or physiological responses [24,36,37]. On the other hand, only a few studies have focused on assessing the adverse effects of long-term BFR training [33,38,39,40]. Therefore, given the growing interest in the BFR method in various human populations, verification and documentation of safety become urgent.
The phrase “blood flow restriction” includes nearly 11,000 articles in PubMed, and adding “safety” reduces that number to 254. A significant part deals with theoretical considerations, literature reviews, and meta-analyses; excluding those studies from the search, only 34 original articles devoted to the BFR resistance training safety remain. Therefore, in comparison to studies evaluating the efficiency of BFR in terms of physical performance and body composition changes, there is still a paucity of empirical studies concerning safety, especially regarding ocular health. Nonetheless, studies to date report negligible adverse effects due to the use of BFR [41,42,43]. Probably the largest survey was conducted in 2005 [41] and repeated in 2016 [42] in Japan. In each, responses from over 12,000 participants from 105 and 232 facilities were collected, respectively. The first study found an incidental occurrence of serious side effects as follows: venous thrombus (0.055%), pulmonary embolism (0.008%), and rhabdomyolysis (0.008%). However, in the latter, such side effects were not noticed. This may mean that knowledge about BFR training is gradually increasing, reducing the risk of severe side effects. In 2011, Leonneke and colleagues [44] summarized the safety of BFR training, pointing out that possible concerns may be related to training-induced alternations in cardiovascular functions and the peripheral nervous system. Attention is also paid to the potential increased oxidative stress or the response of antioxidant enzymes [45], and muscle damage [43,46]. Considering ocular function, BFR resistance training may indirectly impact changes in systemic vascular pressure. Hypoxia and accumulation of metabolites in active muscle during BFR resistance training might augment the metaboreflex resulting in increased blood pressure. This is supported by evidence showing that regular BFR resistance training significantly increases blood pressure compared to traditional resistance training [47,48,49]. In addition, this phenomenon might be pronounced in hypertensive individuals [48]. However, it is possible that the blood pressure changes could be pressure-dependent. The pilot study by Maciel et al. [50] reported an acute reduction of blood pressure after BFR resistance training at 60% of arterial occlusion pressure (AOP) but increased systolic blood pressure by 15 mmHg after BFR with 80% of AOP. Nonetheless, high and low blood pressure is associated with an increased risk of glaucoma [51].
Although using BFR during resistance training seems feasible for glaucoma patients or those at risk of glaucoma, some issues must be investigated and resolved. First, although the effects of resistance training on ocular health have been studied [11,12,13,52], there is only one pre-preliminary study using BFR [14]. In addition, this study examined BFR without resistance exercise and with a short restriction duration (only 40 s) using both high (60% AOP) and low pressures (40% AOP) in the upper and lower limbs [14]. BFR without exercise with such short restriction times is not an often-used approach, and recent recommendations indicate that the duration of the restriction should be between 5–10 min per exercise [29]. Nevertheless, a study by Vera et al. [14] provides interesting results that are worth discussing from the perspective of future research. Authors found that IOP and ocular perfusion pressure did not change significantly during BFR applied on lower limbs with both high and low pressure as well as during upper limbs with low pressure (no difference between sexes). However, high-pressure upper limbs BFR induced a significant increase (for both sexes) in IOP and decreased ocular perfusion pressure (only for men). Moreover, only relatively lower AOPs (a measure used to prescribe intensity of restriction) during BFR were examined, while a greater level of 80% falls within the current recommendations [29]. Overall, it seems that an increase in IOP due to BFR might depend on the applied pressure and place of application, while decreases in ocular perfusion pressure could be sex-dependent. Most importantly, the long-term effects of BFR on vision health are unknown.
This entry is adapted from the peer-reviewed paper 10.3390/jcm11164881
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