The effects of magnesium supplementation on blood pressure (BP) have been studied for over 25 years and results have been inconsistent. Blood pressure reductions in randomized studies have varied from 12 mmHg reductions to no reduction. The objective of this pilot intervention was to investigate the effect of magnesium supplementation on systolic blood pressure whilst resting and during recovery from aerobic and resistance exercise and on performance. A further objective was to see whether the effect of a high vs low habitual dietary magnesium intake affected these results. Sixteen male volunteers were randomly assigned to either a 300 mg·d^-1 magnesium oxide supplementation (MO) or a control group (CG) for 14 days. Resting blood pressure (BP) and heart rate (HR) were measured before subjects performed a maximal 30 minute cycle, immediately followed by three x 5 second isometric bench press, both at baseline and after the intervention. Blood pressure and heart rate were recorded immediately post exercise and after five minutes recovery. A 3 day food diary was recorded for all subjects to measure dietary magnesium intake. At the end of the intervention, the supplemented group, had a reduction in mean resting systolic BP by 8.9 mmHg (115.125 ± 9.46 mmHg, p = 0.01) and post exercise by 13 mmHg (122.625 ± 9. 88 mmHg, p = 0.01). Recovery BP was 11.9 mmHg lower in the intervention group compared to control (p = 0.006) and HR decreased by 7 beats per minute in the experimental group (69.0 ± 11.6 bpm, p = 0. 02). Performance indicators did not change within and between the groups. Habitual dietary magnesium intake affected both resting and post exercise systolic BP and the subsequent effect of the magnesium supplementation. These results have an implication in a health setting and for health and exercise but not performance.

• Magnesium supplementation will have an effect on resting and recovery systolic blood pressure with aerobic exercise.

• Magnesium supplementation will have an effect on resting and recovery systolic blood pressure with resistance exercise.

• Magnesium supplementation did not have an effect on performance indicators.

• A low habitual dietary magnesium intake will negatively affect blood pressure.

• A high habitual dietary magnesium intake will impact on the effect of magnesium supplementation.