Heavily taxed heart beats more slowly with fish oil

Fish oil may help to improve performance during extreme aerobic exercise, when the heart is performing at its peak ability. We deduce this from a study done by sports scientists at the Australian University of Wollongong. The researchers discovered that the heart beat less quickly during intensive exercise in subjects that had been given fish oil supplements.

Heavily taxed heart beats more slowly with fish oil

The researchers hit upon the idea of giving athletes fish oil because they found evidence in the literature that ordinary mortals’ hearts beat slower when they take fish oil supplements. If the same effect is found in athletes, fish oil might help enhance performance. To see if this was indeed so, the researchers did an experiment with sixteen trained male cyclists. They were given a daily dose of 3.2 grams of omega-3 fatty acids in the form of fish oil capsules, for a period of eight weeks. A control group was given a placebo instead. The athletes were given eight capsules a day, each containing one gram of tuna fish oil.

After eight weeks the researchers got the test subjects to cycle. When the athletes cycled for an hour at 55 percent of their VO2max, the ones who had taken a supplement consumed less oxygen.


The researchers speculate that this is because the fish oil makes the slow muscle tissue more sensitive to insulin. That helps them absorb glucose more easily from the blood.

This effect is not particularly interesting for athletes. What is interesting, is the effects of the supplement that come into play when the athletes cycle at very high intensity. In a test where the athletes had to cycle at an increasingly fast rate, the ones who had taken fish oil had a slower heartbeat. The effect is shown in the table below. The effect becomes smaller, the more watts the athletes have to produce, but there is still an effect.


The graph below shows the difference in heart rate before the experiment started and after eight weeks of taking fish oil.


The researchers note that “this study did not attempt to link fish oil supplementation to altered exercise performance”. The experimental set-up was not suitable for this they say. But even if the researchers are not prepared to say anything about performance enhancing effects of fish oil, it doesn’t mean that the effect isn’t there.

Fish oil reduces heart rate and oxygen consumption during exercise.


Dietary omega-3 polyunsaturated fatty acids (PUFAs) are readily incorporated into heart and skeletal muscle membranes where, in the heart, animal studies show they reduce O2 consumption. To test the hypothesis that omega-3 PUFAs alter O2 efficiency in humans, the effects of fish oil (FO) supplementation on O2 consumption during exercise were evaluated. Sixteen well-trained men (cyclists), randomly assigned to receive 8 x 1 g capsules per day of olive oil (control) or FO for 8 weeks in a double-blind, parallel design, completed the study (control: n = 7, age 27.1 +/- 2.7 years; FO: n = 9, age 23.2 +/- 1.2 years). Subjects used an electronically braked cycle ergometer to complete peak O2 consumption tests (VO 2peak) and sustained submaximal exercise tests at 55% of peak workload (from the VO 2peak test) before and after supplementation. Whole-body O2 consumption and indirect measurements of myocardial O2 consumption [heart rate and rate pressure product (RPP)] were assessed. FO supplementation increased omega-3 PUFA content of erythrocyte cell membranes. There were no differences in VO 2peak (mL kg(-1) min(-1)) (control: pre 66.8 +/- 2.4, post 67.2 +/- 2.3; FO: pre 68.3 +/- 1.4, post 67.2 +/- 1.2) or peak workload after supplementation. The FO supplementation lowered heart rate (including peak heart rate) during incremental workloads to exhaustion (P < 0.05). In addition, the FO supplementation lowered steady-state submaximal exercise heart rate, whole-body O2 consumption, and RPP (P < 0.01). Time to voluntary fatigue was not altered by FO supplementation. This study indicates that FOs may act within the healthy heart and skeletal muscle to reduce both whole-body and myocardial O2 demand during exercise, without a decrement in performance. PMID: 19034030 [PubMed - indexed for MEDLINE] Source: http://www.ncbi.nlm.nih.gov/pubmed/19034030

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