|While Mg2+ deficiency can cause leg cramps it is in practice rarely the main culprit, dehydration & a lack of salt are more common (Schwellnus. 2008).|
Still, some studies have shown that Mg 2+ may have a positive effect on sporting performance (Lukaski, Bolonchuk, Klevay, Milne & Sandstead, 1983; Brilla & Haley, 1992; Brilla & Gunter, 1995). Oftentimes however without previously determining whether the subjects had low magnesium levels.
Brilla and Gunter (1995), for example conducted a double blind four week cross-over design study on 20 females and 12 males (recreationally active). After consumption of either placebo or Mg 2+ supplementation (314mg/day), subjects completed an exercise trial which involved performing contractions on an isometric leg dynamometer until exhaustion. After another four weeks supplementation subjects returned for a second isometric leg trial to exhaustion. As Pitkin points out in his recent masters thesis, the authors
"reported that there was a significant increase in time to fatigue when Mg2+ was compared to placebo. This may suggest that Mg 2+ is effective in increasing the time to fatigue on a leg dynamometer.
Figure 1: There is a relationship between VO2 max and fasting plasma Mg2+ athletes (Lukaski. 1983)
[However,] Brilla and Gunter (1995) failed to provide subjects with a washout period between interventions which may have had a negative effect on recorded results as levels of Mg2+ may not have returned to baseline level for the group experiencing placebo as their second intervention" (Pitkin. 2014).Now, that's old news. What's really interesting, though, are the results of Pitkin's very own study that was determined to determine if there is a significant effect on blood pressure, serum levels of magnesium and sports performance including 1RM and 10 kilometre running time trial following Magnesium (Mg2+) supplementation over a five week intervention period in recreationally active athletes when compared to a 5 week placebo intervention.
The design of the study involved the participants completing the protocol a total of four times over a fourteen week period. Participants were tested initially as a baseline measurement. Subjects were then provided with supplementation, either 500mg/day of placebo or magnesium which was picked at random, resulting in 8 subjects initially consuming placebo and 5 subjects consuming Mg2+.
"Subjects participated in a 14 week protocol which employed a randomized blind cross over controlled design. Fifteen subjects were initially screened and accepted for participation. During the protocol two subjects dropped out, failing to complete. This left nine male and four female subjects who were successful in completing the protocol (Age: 24.85 ± 6.49 years, Height: 175cm ± 10.34 cm, Weight: 71 .9 Kg ± 11.46 Kg)" (Piktin. 2014).
Table 1: Characteristics of the 13 studied participants (Pitkin. 2014)
The study used a cross-over design, which means that both subjects took the MG or placebo supplement for 4 weeks. In view of the low number of participants this is a major advantage which makes the results that were evaluated at the end of the two supplementation phases that were interspersed with a wash-out period more reliable.
"After the four week supplementation period participants returned to the University to have post intervention testing conducted. Following this, participants had a five week washout period aiming to reduce any potential performance gains attained from the intervention and bring subjects back to baseline levels. After the washout period participants returned for a third time to complete a second set of baseline testing, participants were then presented with their second intervention" (Pitkin. 2014).
Table 2: Overview of the study design (Piktin. 2014).
|Figure 2: Average completion time recorded for all subjects‟ pre and post Mg2+ (Pitkin. 2014)|
The low magnesium levels are particularly interesting, because the value did not increase into the "normal" range over the course of the supplementation phase. This puts a huge "?" behind the assumption that magnesium intakes that would be normal for Average Joe's are sufficient for athletic individuals. On the other hand, the mean Mg2+ intakes of the subjects were 274.77mg ± 113.15mg/day for the male and 251.25mg ± 47.39mg/day for the female participants and thus not exactly as high as one would like to see them (380mg+). In spite of that, scientists have long suspected that endurance trainees in particular would have an increased need for Mg2+ due to its catabolism as a consequence of to the high habitual daily rates of energy expenditure (Terblanche et al., 1992). Convincing evidence that this is actually the case is however still lacking - specifically because the loss of magnesium in sweat has often been extremely overestimated.Even the small increase of 0.02 (3.7%) mmol/L that was also seen over the course of the Mg 2+ supplementation was yet sufficient to trigger an average decrease in 10K completion time of exactly 1 minute (1.77%) - a performance advantage with both statistical and real world significance, which went hand in hand with lower heart rates during the 10k run in the MG vs. placebo group (normally you would expect higher heart rates with increased performance if the magnesium supplement did not improve the work efficacy of the heart).
|Figure 3: Changes in mean power during the bench press test at different % of the 1-RM before and after the 10k-run during the placebo and magnesium supplementation phase (Pitkin. 2014).|
|Metabolic pathways for ATP muscle contraction & relaxation (Jupp. 1993).|
|Figure 4: Average diastolic blood pressure (mmHg) recorded after the completion of the running time trial at pre and post both Mg 2+ and placebo interventions; data from both groups (Pitkin. 2014)|
Similar reductions were observed for the diastolic blood pressure before and after the run (see Figure 4). For athletes that's probably not relevant, but for the average weekend warrior who may well be suffering from elevated blood pressure, this "side effect" may be highly welcome.
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