ACSM 2010 Review - Nutrition

[Guest guest]

Excerpts provided:

Chocolate Milk and Other Strategies for Athletes at the 2010 ACSM Annual Meeting

Will G Hopkins

Sportscience 14, 22-28, 2010 (sportsci.org/2010/wghACSM.htm)

Nutrition

There's little doubt that dietary antioxidants can reduce the signs and symptoms

of the oxidative stress of hard or eccentric exercise, but do they benefit or

harm athletic performance acutely, and do they benefit or harm adaptations to

training when consumed chronically? Few of the many studies on antioxidants

presented at this conference addressed these questions. One of the best was a

crossover study of 23 female runners, who performed three 3-wk blocks of

overload training each followed by a taper and performance tests, with

consumption in each block of an isocaloric drink containing either blackcurrant

extract, megadoses of vitamin C, or placebo, with 4-wk washouts and performance

pretests before each block to adjust for individual changes in performance over

the extended period of the study [2902]. The training consisted of

high-intensity intervals performed competitively on a hilly course, and the

performance tests after each taper were a treadmill incremental test and a 5-km

road time trial. Vitamin C and blackcurrant extract impaired training intensity

clearly by ~1%, but in spite of the large sample size and sophisticated

analysis, mean effects on the performance tests were unclear (i.e., possibility

of small beneficial effects but unacceptable risk of small harmful effects). Not

stated in the abstract was some evidence that faster runners might benefit from

the blackcurrant. It's possible that there were beneficial acute effects from

the antioxidants on the day of the tests that were offset by harmful chronic

effects on training, an issue with many such studies that needs to be resolved.

There were several studies of effects of other botanical antioxidants on

performance or recovery. Two weeks of an " almond diet " or " almond and purple

sweet potato leaves diet " resulted in 46% and 39% increases in run time to

exhaustion respectively at 75% VO2max compared with the ~34-min control (not

placebo) in 14 male team-sport athletes [2905]. In contrast, 7 d of

supplementing with pomegranate juice (not stated as such in the abstract) vs

placebo resulted in a reasonably clear 4.5% impairment of mean power of 12

endurance athletes in a 10-min cycling time trial in the heat [2904], even

though pomegranate juice reduced muscle soreness and weakness following

muscle-damaging eccentric exercise in 17 (9+8?) resistance-trained males [1931].

Two supplements with antioxidant activity (one based on rose hips, rhodiola, and

astaxanthin; the other based on ashwaganda, prickly pear, and grape seed) also

reduced strength loss following eccentric exercise in 31 healthy men randomized

to the control and treatment groups [1747]. Another herbal blend (Rhodiola

crenulata and Cordyceps sinesis) might enhance the effects of altitude

training, but statistical significance in the treatment group and not in the

control group probably means nothing useful [1936].

Quercetin ( " kwer-sitin " ) was the main topic of one of the two President's

Lectures that closed the conference [no abstract]. Mark painted a very

rosy picture of a compound found in fruits and vegetables that at least in

animal studies has all manner of beneficial effects on performance, immunity,

and even colon cancer, mediated possibly through anti-inflammatory,

anti-oxidant, and caffeine-like actions. Effects on humans might not be so clear

cut, according to the Wikipedia article, and at this conference there was only

one arguably beneficial effect–a reduction in post-exercise blood pressure–in

seven abstracts of studies of quercetin and related compounds [2567-2574]. Mark

cited one study in his lecture showing an increase in VO2max and time to

exhaustion in humans, but the subjects were untrained and did not train during

the 7 d of supplementation.

I was intrigued to attend Russ 's colloquium on antioxidants in

exercise [no abstract], because Russ has done outstanding work in the past on

delivery of oxygen as the limiting factor in endurance performance. He has now

grafted this prior interest onto the effects of aging and antioxidants on the

delivery of blood to muscle. In summary, an acute dose of antioxidants restores

the age-related loss of vascular function, but the partial restoration that

occurs with training in old muscle is antagonized by antioxidants. His

observations fit with the emerging picture of antioxidants as worth taking

acutely for competitive performance but bad for training, as his co-presenter

Vina recommended. Russ had no answer to my question as to whether dietary

antioxidants antagonized blood flow to the brain in aging professors who

exercise and mega-dose on blueberries and blackcurrants.

Fish oil has anti-inflammatory properties, but supplementing for 65 d in a blind

controlled trial apparently had little effect ( " all P>0.05 " ) on markers of

inflammation, muscle damage and muscle strength following a subsequent acute

bout of eccentric exercise [2829]. With only 10+10 " participants " (5 females

and 5 males in each group), the study was probably underpowered for conclusions

about small or trivial effects, but exact p values–or better still, confidence

limits–would help savvy readers decide. This comment applies to the majority of

all the presentations. Sigh…

A drink containing fructose and maltodextrin was absorbed more rapidly than an

isocaloric drink containing only maltodextrin in a crossover with 14

cyclists/triathletes; performance of a 60-km time trial following a 2.5-h

preload was substantially better with the fructose, although " no significant

differences were found " [857].

A newly designed hypotonic sports drink (Mizone Rapid) was absorbed more rapidly

than drinks that were isotonic (Powerade), mildly hypertonic (Gatorade) or

strongly hypotonic (water placebo) in a crossover with 11 cyclists/triathletes;

the observed effect on performance in an incremental test following a 2-h

preload was best with the hypotonic drink (by 1.2%), but there was too much

uncertainty for the outcome to be clear [860].

Hyperhydration with glycerol had practically zero effect relative to a water

placebo on a ~1-h running time trial in the heat, but you'd need more than the 6

runners in the crossover to rule out substantial differences [1682]. A similar

study of the effects of sodium loading with or without glycerol in 8 endurance

athletes (a messy mix of 7 males and 1 female) was similarly inconclusive

[1684].

Meta-analysis of the effects of hypohydration showed that it starts to affect

endurance performance when loss of body mass is 3% or more, but there was no

mention of ambient temperatures in the studies [1679]; hypohydration also

impaired some kinds of shorter performance, but a threshold was less clear

[1681]. There was one original-research study showing unsurprising impairment

with hypohydration [1683].

It's reasonably clear that rinsing the mouth with sugar solutions enhances

performance, and now it looks like mouth rinsing with water enhances cycling

performance in dehydrated subjects. The only difference is that you have to

swallow the water, apparently to activate receptors in the throat [943]. The

quantities are too small for the effect to be mediated via any offsetting of the

dehydration. There's no real relevance to athletes here, of course, but it's

quirky enough to include in this report.

Chocolate milk for recovery! After a fatiguing bout of exercise lasting nearly

2 h and finishing with intervals, 10 trained cyclists (5 M and 5 F) recovered

for 4 h while drinking chocolate milk or an isocaloric carbohydrate drink in a

crossover fashion before a 40-km time trial, which they performed an astonishing

8.4% faster on the chocolate milk [2816]. The authors opted for faster glycogen

resynthesis as the explanation, but what about chocolate receptors?

Adding protein to a drink containing maltodextrin and fructose if anything

impaired performance of a 60-km time trial following a 2.5-h preload, but there

were only 7 cyclists/triathletes in the crossover, and no data in the abstract

beyond " P>0.05 " [1575].

When 15 Aussie-rules football players consumed branched-chain amino acids with a

meal 3 h before fatiguing exercise, they experienced less fatigue-related

decrements in exercise and skill performance in subsequent sport-specific tests,

in comparison with the meal alone [2864]. The effect was small but clear, so

BCAAs might be worth using before important competitions. As for the mechanism,

BCAAs apparently compete with tryptophan for uptake into the brain, where

tryptophan is converted to fatigue-inducing serotonin. Sure enough, when amino

acids were switched to a mixture aimed at enhancing tryptophan uptake, fatigue

was worse. Nice one, Nigel (Stepto)!

â-alanine is an amino acid in meat that gets taken back up into meat (muscle)

when you eat it. There it is converted to carnosine, which acts as an

intracellular buffer. On the Friday at lunchtime Powerbar launched a new

sustained release â-alanine supplement that will make loading over a month or so

much easier and probably more effective. The evidence for performance

enhancement in bouts of high-intensity exercise lasting several minutes is

already clear cut, and a study showing positive effects that are further

augmented with acute bicarbonate supplementation was presented that afternoon

[930]. Useful information about dosing and time course of loading was also

presented [929]: you can speed up the loading with higher doses, and it takes

weeks to wash out.

â-hydroxy â-methylbutyrate (HMB) is an amino acid with likely anabolic effects

in muscle, but the abstracts at ACSM were a mixed bag: it works on retaining

strength and muscle mass in aging rats [2856–a clever study], but it didn't

enhance training in old rats [2858], nor did it protect against the effects of

eccentric exercise in old humans [2857].

Training for 28 d with creatine supplementation produced a possible enhancement

of jumping performance in 6+6 highly trained volleyball players, although data

of only 8 players were in the final analysis [1917].

Bicarbonate supplementation worked for short swimming sprints, by a massive 2%

in a crossover with 6 male and 8 female swimmers and a test designed to

emphasize competition and eliminate turns [1923].

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Carruthers

Wakefield, UK