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Swimming after eating

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chris.hunter
339098.  Sun May 18, 2008 6:28 pm Reply with quote

QI on Friday 16th of May stated that it was a myth that swimming after eating posed a higher risk of cramp and drowning. I am pretty sure that this is wrong. When you eat a significant proportion of your cardiac output is diverted to your splanchnic circulation to digest food, reducing the amount of blood flow and therefore oxygen available to voluntary muscle for swimming. Reference:British Journal of Nutrition (1994), 71, 835-848 835The effect of meal size on the cardiovascular responses
to food ingestionBY MICHAEL B. SIDERY AND IAN A. MACDONALD

Cardiac output (CO ; indirect Fick), blood pressure (BP) and heart rate (HR; oscillometry), superior
mesenteric artery blood flow (SMABF; Duplex Doppler) and calf blood flow (CBF; venous occlusion
plethysmography) were recorded in the fasted state and for 120 min following the ingestion of 1, 2, and
3 MJ, high-carbohydrate meals in eight healthy females. BP was unchanged following food. HR
(P < 0.0005) and CO (P < 0.005) rose significantly following all three meals. Integrated increments in
CO over the postprandial period were greater after 3 MJ compared with the 1 and 2 MJ meals
(P < 0.05). SMABF rose significantly following all three meals. The pattern of blood flow response was
significantly different between the 1 and 3 MJ meals (interaction effect P < 0.02, ANOVA), with blood
flow after the 3 MJ meal being significantly greater than flow after the 1 MJ meal at 15,60, and 90 min.
Similarly, the pattern of response was significantly different after the 2 and 3 MJ meals (interaction
effect P < 0.03, ANOVA), with blood flow being significantly greater at 15 and 90 min after the 3 MJ
meal. CBF fell significantly in the first 15 min after the 3 MJ meal and then recovered towards baseline
values. No other significant changes in CBF were recorded. There are substantial peripheral and central
cardiovascular changes after food in man and there appears to be a relationship between meal size and
the extent of these changes.

 
Flash
339110.  Sun May 18, 2008 6:49 pm Reply with quote

Thanks, Chris. There seems to be a bit of a disconnect between the research you cite and the conclusion you draw, though. Is there evidence that:

1) the effects described cause cramp? and
2) if they do, that the cramp causes drowning? Why wouldn't one simply grimace and wait for the cramp to pass?

Furthermore:

3) is there a single instance of this having actually happened to anyone?

 
CB27
339326.  Mon May 19, 2008 6:36 am Reply with quote

I think it's unlikely people will get cramp, but it's generally not a good idea people start excercising vigirously after eating a meal as it's likely to make them throw it back up again (and I'm sure lots of people like me will relate one experience or another).

Swimming I would have though is more dangerous than other forms of excercise as you wouldn't want to start heaving whil in the water with the possible repercussions that it can affect your momentary capability to stay calm and afloat.

 
wobs
339386.  Mon May 19, 2008 8:01 am Reply with quote

The only time I've had cramp while swimming was not long after eating.

Do I get a prize?

 
Sadurian Mike
339691.  Mon May 19, 2008 3:21 pm Reply with quote

Flash wrote:
Thanks, Chris. There seems to be a bit of a disconnect between the research you cite and the conclusion you draw, though. Is there evidence that:

1) the effects described cause cramp? and
2) if they do, that the cramp causes drowning? Why wouldn't one simply grimace and wait for the cramp to pass?

Furthermore:

3) is there a single instance of this having actually happened to anyone?

I don't think drowned people tend to write about it in their diaries much.

 
Sadurian Mike
339703.  Mon May 19, 2008 3:28 pm Reply with quote

I've had swimming cramp only once, unconnected to eating. Looking at the research, it seems to simply say that blood flow and CO2 increases after a heavy meal. As the blood carries the CO2 away and both increase simultaneously, the only danger would be if blood flow decreased or didn't increase at the same time as the CO2.

You could layer on top of that the increase in CO2 from exercise, and the simultaneous increase in heart rate. Unless the increase in CO2 outstrips the heart rate, or the heart rate increases to dangerous levels, there doesn't sppear to be a problem.

As CB27 says, there would be more danger in being sick (particularly dangerous using breathing apparatus) than in additional risk of cramping.

 

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