תזונה ותוספים תמונה New strategies in sport nutrition to increase exercise performance.

[Mike Bikov]

Free Radic Biol Med. 2016 Feb 5. pii: S0891-5849(16)00030-7. doi: 10.1016/j.freeradbiomed.2016.01.016. [Epub ahead of print]

New strategies in sport nutrition to increase exercise performance.

Close GL1, Hamilton L2, Philp A3, Burke L4, Morton JP5.
Author information

Abstract
Despite over 50 years of research, the field of sports nutrition continues to grow at a rapid rate. Whilst the traditional research focus was one that centred on strategies to maximise competition performance, emerging data in the last decade has demonstrated how both macronutrient and micronutrient availability can play a prominent role in regulating those cell signalling pathways that modulate skeletal muscle adaptations to endurance and resistance training. Nonetheless, in the context of exercise performance, it is clear that carbohydrate (but not fat) still remains king and that carefully chosen ergogenic aids (e.g. caffeine, creatine, sodium bicarbonate, beta-alanine, nitrates) can all promote performance in the correct exercise setting. In relation to exercise training, however, it is now thought that strategic periods of reduced carbohydrate and elevated dietary protein intake may enhance training adaptations whereas high carbohydrate availability and antioxidant supplementation may actually attenuate training adaptation. Emerging evidence also suggests that vitamin D may play a regulatory role in muscle regeneration and subsequent hypertrophy following damaging forms of exercise. Finally, novel compounds (albeit largely examined in rodent models) such as epicatechins, nicotinamide riboside, resveratrol, β-hydroxy β-methylbutyrate, phosphatidic acid and ursolic acid may also promote or attenuate skeletal muscle adaptations to endurance and strength training. When taken together, it is clear that sports nutrition is very much at the heart of the Olympic motto, Citius, Altius, Fortius (faster, higher, stronger).

 

[kotzer]

דבר אחד לא הבנתי, מה השורה התחתונה פה לגבי פחמימות?

 

[Mike Bikov]

2.2. Is carbohydrate still king?
The principle of ensuring adequate carbohydrate (CHO) availability to promote exercise performance is the foundation of which contemporary sports nutrition practices have typically been built upon. Indeed, the importance of muscle glycogen as a determinant of exercise capacity was first recognized as early as the late 1960 s with the introduction of the muscle biopsy technique into exercise physiology research [34]. Since this landmark study, a wealth of studies conducted over the next 40 years unequivocally confirmed that high pre-exercise muscle glycogen stores (i.e. >500 mmol.kg-1 dw) can improve endurance and team sport performance in those instances where exercise duration is >60−90 minutes [35]. As such, elite athletes are now advised to consume at least 6−12 g/kg body mass of CHO in the 24−36 h prior to competition so as to adequately “CHO load” for competition day [36].

In addition to high endogenous pre-exercise muscle glycogen stores, it is widely accepted that exogenous CHO feeding during exercise also improves physical, cognitive and technical elements of performance [37]. Whereas it was generally accepted that exogenous CHO oxidation rates were thought to be limited at approximately 1 g/min due to saturation of intestinal glucose transporters, it is now known that exogenous CHO oxidation rates can increase to 1.8 g/min with the addition of sucrose or fructose to the CHO blend [38]. When taken together, it is currently thought that CHO feeding during exercise may therefore augment exercise performance via multiple mechanisms consisting of muscle glycogen sparing [39], liver glycogen sparing [40] and maintenance of plasma glucose and CHO oxidation rates [41]. It is noteworthy, however, that exogenous CHO feeding during exercise also improves performance when exercise duration is <60 minutes [42], an effect that is not apparent when glucose is directly infused to the bloodstream during exercise [43]. Such data suggest that CHO feeding may also improve exercise performance via non-metabolic effects but through direct effects on the central nervous system [44]. To this end, the last decade of research has resulted in a growing body of literature demonstrating that simply “rinsing” CHO in the oral cavity (for 10-second periods every 5−10 minutes during exercise) is also ergogenic to performance [45], an effect that is independent of sweetness [46] and that is especially apparent in the absence of a pre-exercise CHO meal [47] and low pre-exercise muscle glycogen [48].

The conventional approach to CHO fuelling during exercise is to consume 6−8% CHO beverages, although relying solely on this approach does not allow for flexibility in terms of individual variations in body mass or actual fluid requirements given variations in ambient conditions [49]. As such, many athletes rely on a CHO fuelling approach that is based on a combination of solids (e.g. bars), semi-solids (e.g. gels) and fluids (e.g. sports drinks) so as to collectively meet their personalized exogenous CHO targets, typically in the region of 30−90 g/h depending on exercise duration [38]. Nevertheless, although there is little difference in exogenous CHO oxidation rates (albeit in fluid matched conditions) between the aforementioned sources [50] and [51], it is noteworthy that many athletes experience gastrointestinal discomfort when attempting to hit these targets, possibly related to extreme differences in osmolality between commercially available CHO gels [52] as well as the presence of fibre, fat and protein in energy bars [53]. As such, it is now advised that athletes should clearly practice their approach to in-competition fuelling during those training sessions of similar intensity and duration as competition [54].

Although CHO guidelines for competition are now generally accepted, considerable controversy exists as to the optimal targets of endogenous and exogenous CHO availability for which to adhere to during both moderate and intensive training periods. Indeed, whilst both low endogenous [55] and exogenous [56] CHO availability can undoubtedly impair training intensity, accumulating data have now demonstrated a potent effect of reduced carbohydrate availability in modulating those acute exercise-induced increase in cell signalling and gene expression responses that regulate endurance training adaptations [57] and [58]. In this regard, we and others have collectively observed that reducing endogenous and/or exogenous CHO availability during short-term (e.g. 3−10 week) endurance training increases mitochondrial enzyme activity and protein content [55], [59] and [60] increases both whole body [55] and intramuscular lipid oxidation [61] and in some instances, improves exercise capacity[62] and [63]. These data have therefore led to the innovative “train-low (or smart), compete-high” model surmising that athletes deliberately complete a portion of their training programme with reduced CHO availability so as to augment training adaptation but yet always ensure high CHO availability prior to and during competition in an attempt to promote maximal performance [64]. The augmented training response observed with training-low strategies are currently thought to be regulated via the enhanced activation of upstream cell signalling kinases including both AMPK [23] and p38MAPK [65] that ultimately converge on the downstream regulation of key transcription factors and co-activators such as PGC−1α [66], p53 [21] and PPARδ [24] (Fig. 1). In this way, training with low CHO availability thereby leads to a co-ordinated up-regulation of both the nuclear and mitochondrial genomes.


Despite the theoretical rationale for the training-low paradigm, potential pitfalls to long-term training with low CHO availability include perturbations to immune function [67]impaired training intensity [55], reduced ability to oxidise exogenous CHO during competition [68] and increased muscle protein oxidation [69]. As such, many challenges remain as to how best to periodise train-low into an elite athlete’s training programme without increasing the risk of the aforementioned maladaptive responses. At present, research studies examining the efficacy of train-low strategies have largely adopted fasted training protocols [60], protein only sessions [70], training twice per day models[62] reducing CHO intake in the post-exercise period [71] and most recently, both sleeping and training (i.e. sleep low-train low models) on the subsequent morning with reduced CHO intake [21] and [72]. Ultimately, the simplest advice at present may be to adopt the practical concept of “fuelling for the work required” in that completing pre-determined training workloads that can be readily performed with reduced muscle glycogen and without exogenous CHO feeding may represent a strategic approach for which to implement day-to-day nutrient-exercise periodization protocols. Alternatively, when the goals of the training session are to complete the highest workload possible, then adequate CHO should be provided in the 24 h period prior to and during the specific training session. Despite many unanswered questions to the precise molecular mechanisms underpinning the enhanced training adaptations associated with training-low as well as optimal practical application models, it is now readily apparent that we can no longer think of CHO as a simple fuel source of which, depletion causes of fatigue. Rather, we must now add the term of’training regulator’ to its known functions.

 

[ברק]

די מעודכן האיור הראשון למרות שלא לגמרי מדויק .

נראה שהכותב רוצה למכור תוספים אז בגלל זה הוא כתב שם BCAA היה צריך לכתוב EAA או אם כבר לאוצין ואני לא בטוח שהHMB נמצא רק שם הוא כמעט בודאות עושה עוד דברים. דברים יותר דומיננטיים מאשר הצד הזה של המסלול.

 

[Denver]

די מעודכן האיור הראשון למרות שלא לגמרי מדויק .

נראה שהכותב רוצה למכור תוספים אז בגלל זה הוא כתב שם BCAA היה צריך לכתוב EAA או אם כבר לאוצין ואני לא בטוח שהHMB נמצא רק שם הוא כמעט בודאות עושה עוד דברים. דברים יותר דומיננטיים מאשר הצד הזה של המסלול.

אני סבור שהוא לא התכוון ל-BCAA מבחינת התוסף עצמו, אלא כשרשרת חומצות אמינו(שיכולה להגיע גם מהמזון) שתורמת לסינטזת חלבון.

 

[ברק]

זהו שהציור לא מספיק ברור אבל בכל מקרה במקום הזה בציור אמורה להיות רק לאוצין. שתי האחרות לא עושות כלום בצד הזה של המסלול ויכול להיות שמפריעות בכלל ללאוצין להכנס לסיב.

בכל מקרה לכל חומצות האמינו החיוניות יש תפקיד נוסף שלא מוזכר כאן הן נכנסות איכשהו לאנדוזום/ליזוזום מחוץ לתא ואז כפי הנראה משאבות הפרוטונים חשות אותן ועוזרות לגייס ולאקטב את Rheb ואת שאר הבלגן.

בכל מקרה חייבים לאכול הרבה חומצות אמינו חיוניות כדי שהתהליך יקרה...