Carbohydrates Flashcards
What key paper looked at CHO utilisation during exercise?
Van loon et al (2004) looked at cho utilisation during exercise in 8 subjects.
During rest, energy just from plasma FFA and plasma glucose
At 40% wmax - majority contribution of EE from plasma FFA and other fat sources
At 55% same trend - with a higher overall EE
At 75% majority from glycogen, and then glucose, fats become less important (plasma FFa still higher)
What did Hermansen et aL (1967) find??
Looked at muscle glycogen during prolonged severe exercise (cycle to exhaustion @77% vo2 in 10 endurance trained men)
- showed glycogen depleted as exercise time increased, all the way to exhaustion
What’s the first paper looking at CHO quantity during exercise on performance?
Bergstrom et al (1967) found a correlation between muscle glycogen and work time (to to exh @75% vo2 max)
-‘those with high CHO diet took longer to reach exhaustion vs med CHO or low CHO
Coyle (1986) looked at CHO ingestion during ex, what did he find?
Had 7 endurance trained cyclists perform cycle to fatigue, with either placebo or CHO
With CHO, they went for 1 hour longer! Despite similar glycogen levels at the point of fatigue. However at this point, blood glucose began to drop and also CHO oxidation began to drop considerably also for the placebo group - suggested could be liver glycogen issue leading to hypoglycaemia and then fatigue.
What evidence is there that muscle glycogen depletion occurs following a marathon??
Gordon et al (1920) found hypoglycaemia following Boston marathon.
Gillum et al (2006) found a 83% reduction in muscle glycogen pre to post race
What evidence is there from games players that glycogen is depleted??
Krustrup et al (2006) - danish footballers and found pre - post there was a 42% reduction in muscle glycogen
Bradley et al (2016) found a 40% reduction pre to post in rugby players
Both studies blood glucose unaffected
Tzintas et al (1996) looked at CHO ingestion during running at 70% vo2 max, what did he find??
CHO had higher muscle glycogen at high intensities in both fibres compared to water
Stellingwerf (2007) looked at cycling at 63% vo2, and CHO ingestion during. What did he find?
Over 3h average, plasma glucose sig higher and plasma FFA sig lower in CHO group compared to control - EE was same.
Also found less glycogen use in type 1 and type 2 fibres with CHO feeding during exercise
What did the review from Newell find??
Found that a study may find evidence of glycogen sparing or not depending on the methodology.
Tszintas, bergstrom and stellingwerf all provide evidence of glycogen sparing
Coyle and Mitchell et al (1989) find no evidence
Jeukendrup et al (1999) looked at the appearance of glucose in the blood, what did he find??
In fasted - all glucose comes from the liver
In hi glucose state - solely comes from fed glucose
In low glucose state - predominantly from fed glucose with a small amount from liver
Gonzalez et al (2015) looked at liver glycogen sparing what did he find??
The glu and suc group non significantly increased their liver glycogen concentration
The control group significantly decreased for liver glycogen concentration
What did Jeukendrup et al (1997) find ?
Looked at CHO feeding during a 40 km time trial.
Found the CHO - electrolyte group to be significantly quicker than the placebo group (~2%)
This conflicted with carter et al 2004
Carter et al (2004) looked at a 40km TT with either a placebo or a 6% maltodextrin solution mouth rinse, what did he find?
Rinsed every 5km, CHO were significantly quicker than placebo (2-3%)
Results suggest a central component -‘central governed model’ - (chambers et al, 2009) showed increased brain activity vs controls
What does Burke et al (2011) consider to be the general daily carb intake guidelines for athletes??
Light - 3-5g/kg/d
Mod - 5-7g/kg/d
High (1-3 h of mod intensity a day) - 6-10g/kg/d
Very high - 8-12g/kg/d
What did Bussau et al (2002) find?
That glycogen depleting exercise prior to CHO loading does not seem to be necessary to achieve high muscle glycogen levels
- a high CHO diet combined with physical inactivity can lead to a super compensated muscle glycogen level within 24 h
What are Burke et al (2011) guidelines for CHO in the hours before exercise?
Before exercise lasting >60 min in duration, look to get in 1-4g/kg consumed 1-4 hours before exercise - should suit individual needs
What are the recommended CHO intakes during exercise (Burke et al, 2011; JEukendrup et al, 2011)
0 min of exercise - none
60 min - 30-60g/h rapidly oxidised forms of CHO
120 mins - 30-60g/h rapidly oxidised forms of CHO
180 mins - up to 90g/h multiple transportable CHO’s
Jeukendrup and Jentjens (2000) looked at the oxidation of ingested CHO (exogenous oxidation), what did they find?
Exogenous CHO oxidation rate tapers at around 1g/min where CHO ingestion rate is around 1g/min (even at 2g/min exo ox stays at 1g/min)
Fructose alone is the worst oxidised, but when added to glucose - can increase peak oxidation rates compared to just glucose alone due to absorption kinetics
Looking at refuelling, what did Costill et al (2017) find??
Looked at daily recovery following 2hrs of ex at 70% Vo2 max.
Muscle glycogen concentration was higher in those who had a high CHO diet than those with a low diet. Post ex - both dropped but the high CHO recovered their muscle glycogen better
What did Ivy et al (1988) find??
When fed CHO, Glycogen synthesis is very high immediately post exercise, when fed CHO 2 hours post exercise, the glycogen synthesis was much lower - get CHO asap for optimal resynthesis
Bradley (2017) built on Ivy’s work, what did he find??
Simulated a rugby league match and gave immediate or 2h delayed CHO feeding.
Showed muscle glycogen storage in 48h post simulation sig better when fed the CHO early.
What did Burke et al (2011) find when looking at short term post-ex muscle glycogen synthesis??
Showed CHO at rates of 1-1.2 g/kg bm/h will optimise short term post ex muscle glycogen synthesis
What did Blom et al (1987) find??
Looked at glycogen synthesis following single nutrient feedings , found foods rich in mod-high GI CHO provide a readily available source of substrate for glycogen synthesis(is no fructose)
In a unique study by Cramer et al (2015) what did he find??
Post ex glycogen recovery is no different between fast food and sports supplement powders - showing if the availability is limited, something is better than nothing.
It’s supposed that PRO can improve muscle glycogen synthesis, what did Burke et al (2011) find regarding this?
When CHO intake is suboptimal (<1/1.2g/kg/h) then protein co-ingestion of 0.4g/kg/h can help increase muscle glycogen synthesis supposedly by an increased insulin secretion leading to increased glycogen synthase
What did Burke et al (2011) suggest were the guidelines for carb intake in the days before exercise???
General fuelling up - prep for events lasting <90 mins - 7-12g/kg/d
Carb-loading - prep for events lasting >90 mins - 36-48h of 10-12g/kg/d
