An informative paper was recently published canvassing peer reviewed research in MMA covering a host of topics from weight cutting, to performance metrics to injury data and more.
The paper, titled Exploratory Systematic Review of Mixed Martial Arts: An Overview of Performance of Importance Factors with over 20,000 Athletes, covers much of what is known about MMA from a research perspective and where more research is needed.
In addressing peer reviewed data about rapid weight cut health and safety issues the researchers highlighted many known problems with the following sobering list "death...muscle damage...decreased performance...emotional and mood disturbances...cognitive impairment...reductions in muscle strength...reductions in aerobic fitness...reduced plasma and blood volume...decreased myocardial efficiency...reductions in blood fluid...reductions in renal function and the volume of fluid filtered by the kidneys...reductions in glycogen stores....impairment of thermoregulatory processes and electrolyte balance...physiological damage to mental function by generating deficits in concentration, memor cognitive processing speed and an increased risk of developing eating disorders."
The full paper is worth reading for its comprehensive discussion on peer reviewed literature addressing MMA. The full discussion on rapid weight cutting is as follows:
Rapid weight loss (RWL) is a common strategy used by MMA athletes to reduce their
body mass (BM), aiming to reach the limit of weight division. The process of RWL usually
starts one/two weeks before competition, and the athletes lose 2–10% of their BM.
The prevalence of RWL among MMA athletes is between 88% and 95%, with
greater predominance among professional athletes compared to amateurs. In contrast
to grappling modalities, such as judo, Malliaropoulos et al. reported in their study
with British judo athletes a prevalence of RWL of 84%. Moreover, the RWL incidence in
MMA is higher than other combat sports. Barley et al. reported a reduction
of 9.8 ± 7.9 kg of BM, while Santos-Junior et al. reported a reduction of ~10%. Many
methods were self-reported by the athletes to induce RWL. For instance, Andreato et al.
found the use of diuretics, saunas, and exercise in hot rooms as main methods used to cut
weight, while Santos-Junior et al. reported the use of a combination of gradual diet
(64.2%), restricting fluid intake (62.6%), and sweat suits (55.9%). Moreover, athletes reported
the use of more aggressive methods such as diuretics (~49%) and laxatives (~32%).
Recently, Connor and Egan also reported using water loading and hot clothing alternative baths as a common method to perform RWL by amateur and professional Irish athletes.
The frequencies of "always" or "sometimes" in surveys were reported as 90% for water
loading and 76% for hot salt baths. Interestingly, Connor et al. compare the use
of hot baths with and without salt, but no differences in the magnitude of weight lost as
found. Subsequently, Connor and Egan reported no differences between a hot freshwater
bath (FWB) and a hot bath with ~1.6% Epsom salt added (SWB) for body mass loss. The
authors state that hot baths lasting 2 h are an effective method of losing ~2.0% RWL body
mass. Some authors also investigated the source of information to induce RWL. The
athletes cited magazines, social networks, coaches, training partners, friends, and physical
trainers as sources, although some mentioned a nutritionist service
The inducement of hypohydration is the primary reported method to provoke RWL
and has significant adverse effects, as it can cause psychology, physical, or health
decline. The reduction in bodily fluids resulting from exercising in hot environments, using plastic clothing, laxatives, and diuretics, might generate electrolyte imbalances, especially calcium, which might lead to less bone mineralization and cause stress
fractures. Additionally, the use of diuretics produces hypokalemia, which is the reduction in body potassium in the blood, altering the activity of the sodium–potassium pump,
which can lead to death. Physiological disturbances on hydration status, hormonal
balance, and markers of muscle damage were also reported. In addition, a decrease on performance, emotional and mood disturbances, and cognitive
impairment. The literature has reported reductions in muscle strength levels, aerobic
fitness, reduced plasma and blood volume, decreased myocardial efficiency and maximal
oxygen consumption, reductions in blood fluid, renal function and the volume of fluid
filtered by the kidneys, reductions in glycogen stores, impairment of thermoregulatory processes, and electrolyte balance. Additionally, RWL is reported to cause
physiological damage to mental function by generating deficits in concentration, memory,
cognitive processing speed, and an increased risk of developing eating disorders.
The negative influence on physiological, physical performance, or psychological
markers due to RWL remains, even after 24 h of recovery. These problems might
occur regardless of the time interval between weigh-in and the fight itself, as physiological
parameters such as hydration status, salivary nitrate, and energy availability may not be
restored enough. Possibly, this behaviour is encouraged by the time between
the official weigh-in and the fight (i.e., 12 to 32 h), which allows for weight recovery so that
an athlete fights one to two categories above the official weigh-in.
There is no consensus on the effect of BM recovery on the fight outcome. The act of weight regain (WR) after weigh-in is reported as a common act among wrestlers of both genders with no differences (p < 0.005) between relative values of BM gains between genders. Kirk et al. showed that the magnitude of the WR does not predict victory or defeat in a professional cohort of MMA athletes. Alternatively, Coswig et al. found that the magnitude of WG was greater in winners than losers, which was more important than the magnitude of RWL. It is important to highlight that the winners showed higher total caloric intake and absolute intake (g) of carbohydrates, proteins, and lipids during the WG than losers, which might partially explain the result. Faro et al. demonstrated that regardless of gender, fighting category, or competitive level, the percentage of WG can be used as a predictor of competitive success in the fight; every 1% of additional WG increases the probability of competitive victory by 4.5%. Figure 3 presents the main findings regarding weight loss in MMA athletes
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