4.1.1. Carbohydrate Manipulation
Carbohydrate manipulation strategies followed a similar pattern to classic CHOL, with three days of restriction, followed by three days of CHOL [
9,
17]. Although competitors did not indicate if they altered their exercise routine during the restriction phase, bodybuilders are known to employ high volume resistance training during this period [
8]. The addition of exercise alongside CHO restriction aims to deplete muscle glycogen, as skeletal muscle lacks glucose-6-phosphotase and therefore cannot contribute to maintaining blood glucose [
18]. Furthermore, CHOL following CHO depletion may result in greater glycogen synthesis activity, enhanced glucose transport, and increased muscle glycogen supercompensation (MGS) [
19]. Moreover, studies in animal models indicate greater upregulation of glycogen synthase and glucose transporter type 4 mRNA, following glycogen depletion; while depleted muscle tissue has increased insulin sensitivity over 48 h dependent on the initial glycogen content [
20,
21,
22]. Energy intake is inevitably reduced as a consequence of CHO restriction. It may therefore be prudent for bodybuilders to increase their fibre and protein intake during this phase as a way of compensating for the loss of energy and the additional satiating effect associated with these nutrients [
23].
Carbohydrate intakes of 8 to 10.5 g/kg BW per day during CHOL have been demonstrated to produce MGS [
18,
24]. This equates to a CHO intake 600 to 785.5 g, or 1800 to 2362.5 g over three days for a 75 kg bodybuilder. Interestingly, three competitors who quantified their CHOL regime achieved an intake greater than or equivalent to these levels. While bodybuilders may wish to take a more conservative approach to CHOL to prevent “spilling over” (too much CHO is thought to result in a watery looking physique) [
11,
12]; lower CHO intake may be inadequate to achieve MGS. It is worth mentioning that traditional CHOL regimes may not perfectly translate from endurance sport to bodybuilding, e.g., marathon runners are not concerned with CHOL’s effect on physical appearance. Conversely extending exercise output is not the goal of a competitive bodybuilder; rather it is full, dry looking muscles. High GI CHO was prioritised at the start of CHOL, before competitors reported moving onto lower GI sources. Carbohydrate loading strategies varied, although, “front-loading”, where most of the CHO was consumed initially, was the most prevalent. This front-loading and the initial use of high GI CHO reflect the notion that glycogen synthesis and storage may be greater in the initial hours following glycogen depletion [
20,
21,
22]. Front-loading may also suggest a pragmatic approach as bodybuilders seek to reduce CHO intake closer to competition to reduce unnecessary gastrointestinal or psychological stress associated with peaking [
8].
Modified, and single day CHOL combined with high intensity sprint exercise, has also been demonstrated to be effective at producing MGS [
25,
26]. One-day protocols could be utilised by bodybuilders and their practicality requires consideration. However, the bodybuilder’s sole goal during peak week is not MGS as multiple variables of the diet and training are manipulated simultaneously. Bodybuilders are aiming to enhance the appearance of muscle size that is thought to be achieved from MGS, while also reducing subcutaneous water, which enhances the appearance of definition. Longer peaking strategies provide bodybuilders with time to adjust their strategies depending on their day to day appearance. Furthermore, conventional bodybuilding wisdom advocates two to three days of rest prior to competition [
11]. Bodybuilders close to competition may therefore perceive the high intensity sprint exercise employed alongside single day CHOL negatively, although if timed correctly, a single bout of sprint exercise is unlikely to result in delayed onset muscle soreness, or loss of isometric capacity. Single day plans would also reduce the interruption to regular training and pre-contest diet seen when weeklong peaking plans are employed. This may allow the competitor to lose more body fat during this time saved in preparation for competition. Single day plans may therefore represent a viable less stressful alternative to the classical approaches currently employed. Finally, loading strategies should consider the athlete’s prior dietary approach and low CHO, high fat diets have been demonstrated to decrease both insulin receptor and glucose transporter type 4 mRNA expression [
27]. Despite these findings, CHOL when employed following acute fat adaptation still results in MGS [
28], although the effect this approach has on the athlete’s physical appearance is unknown.
4.1.2. Water, Electrolytes, and Vitamin C
Bodybuilders manipulate water during peak with the goal of facilitating MGS and removing superfluous subcutaneous water. Water manipulation strategies paralleled CHO manipulation, with high initial intakes followed by a gradual reduction approaching competition day. Previously, Balon et al. [
9] and Reale et al. [
29] noted that between 2.3 to 7.8 mL of water is stored per g/glycogen. This would equate to a requirement of 1000 to 3600 mL of water in a 75 kg bodybuilder with a CHO store of 462 g. When the bodybuilders’ habitual water requirements are considered alongside CHOL, the consumption of additional water to facilitate MGS may be merited. A number of competitors reported consuming between 8 to 12 L of water per day (106.6 to 160 mL/kg of bodyweight, 75 kg bodybuilder) during the loading phase, likely meeting their habitual and CHOL water requirements. Moreover, excessive water consumption causes polyuria, and bodybuilders seek to exploit this diuretic effect, prior to imposing water restriction with the aim of removing any superfluous water [
29,
30]. Bodybuilders, however, should be mindful that skeletal muscle is largely water, and dehydration may negatively affect their appearance, where muscles could potentially end up “flat” looking, lacking in volume or size [
31]. Water manipulation combined with MGS may offer some protection against going “flat”, as muscle glycogen is exclusive for skeletal muscle metabolism. Water bound to glycogen would be retained intracellularly provided the bodybuilder refrained from exercise, although extracellular water may still be lost, negatively affecting appearance. Researchers should however, be mindful that peaking strategies might run counter to traditional sports nutrition practice, and bodybuilders will actively seek to dehydrate themselves to obtain a desired “look” at the expense of metrics, like aerobic or anaerobic performance. The success of peaking strategies should therefore be judged on real-world aspects, such as the bodybuilder’s competition outcome, physical appearance and performance relative to other competitors, and past performances.
Bodybuilders also attempt to remove subcutaneous water via sodium loading and restriction, while it’s worth noting that peak week diets are high in potassium rich foods, e.g., bananas, sweet, and white potatoes. Potassium and sodium are intracellular and extracellular cations, both of which maintain: cellular bioenergetics, integrity, and fluid balance via gated pumps [
32]. Moreover, the renal system regulates fluid balance and osmotic pressure by excreting or retaining sodium and potassium depending on their relative concentrations [
33]. Exercise scientists have long been aware that the addition of electrolytes to water is effective at enhancing hydration [
34], while the depletion of these electrolytes results in a loss of fluid, and a reduction in both blood pressure and plasma volume [
29]. Manipulation of these electrolytes could therefore potentially alter fluid balance and enhance a bodybuilder’s appearance. It was not clear in the present investigation if sodium loading or restricting was the preferred method amongst competitors, although, the “Aceto” peaking method recommends restricting sodium three to four days prior to competition [
11]. It is worth noting though that sodium is required as a cotransporter for the uptake of glucose within the small intestine via sodium glucose linked transporter 1 [
35]. Restriction of sodium three to four days prior to competition may therefore affect the efficacy of CHOL and the subsequent MGS. A lack of consensus amongst competitors on electrolyte manipulation may also reflect the complexity of adding this additional variable to peaking plans, the outcome of which may be difficult to predict alongside CHO and water manipulation.
Finally, bodybuilders reported mega dosing with VITC three to four days prior to competition during the water-loading phase. High VITC consumption is known to stimulate diuresis and bodybuilders use VITC in an attempt to remove excess (subcutaneous) water [
36,
37]. Mega dosing with VITC may cause gastrointestinal issues, while chronic dosing may cause acidification of the urine, and increasing the risk of urate renal stones [
38]. Ascorbic acid and urine excretion increases significantly with dosages of VITC over 200 mg [
39]; it is therefore plausible that bodybuilders may be able to obtain the same diuretic effect with lower dosages than those reported in the current investigation [
39]. Furthermore, employing the diuretic effect of VITC during CHOL and water loading may reduce the efficacy of MGS. Vitamin C loading may therefore be better utilised once the initial CHOL regime is complete to remove subcutaneous water. The consumption of high amounts of herbal tea and protein were other strategies utilised by competitors in an attempt to remove excess water. Such strategies may have some merit as high protein diets are known to increase urea production and glomerular filtration rate both acutely and chronically [
40].