Athletes are on an endless quest to enhance performance and are frequently barraged by products that purport to contribute to various components of athletic activity. These products range from vitamins and herbal supplements to banned substances. Many of the products are poorly regulated and have limited research to support the claims. Despite the fact that magnesium (Mg2+) is the second most abundant cation in the human body, there has been little scientific interest. Part of this issue is the challenge of assessing Mg2+ concentration in the human body. Nonetheless, Mg2+ has several critical functions. It is linked to calcium (Ca2+) movement in and out of the sarcoplasmic reticulum, glycolytic metabolism, enzyme delivery and uptake, adenosine triphosphate (ATP) production, and muscle contraction (7).
In rabbit studies, Mg2+ has been hypothesized to affect crossbridge detachment and force production (1). In studies using frogs (23), Ca2+ transport, a process crucial to muscle contraction, was increased 1.6-fold in the presence of Mg2+. Through the activation of key enzymes in the metabolic pathways, Mg2+ influences multiple components of muscle contraction and relaxation (16).
Custom Prescription Shoppe (Augusta, GA, USA) is the manufacturer of an Mg2+-based cream called MagPro™. This product claims to improve “muscle performance.” However, there is no research to date on the specific aspect of muscle performance that may be influenced by topical Mg2+ application. The manufacturer has made anecdotal claims of enhanced performance, but no one has conducted a randomized, controlled study to establish the efficacy of the product. This study was designed to address 2 of the many components of muscle performance. The 2-phase project involved protocols to assess soft tissue flexibility (stretching) and muscular endurance. The purpose of phase 1 was to determine if the application of MagPro™ (Mg2+ cream) influenced muscle flexibility as measured by passive range of motion. The null hypothesis was that the application of MagPro™ to the gastroc-soleus muscle complex would have no influence on muscle length when accompanied by static stretching. The purpose of phase 2 was to determine if the application of MagPro™ influenced muscle endurance as measured by progressive cycling duration. The null hypothesis was that the application of MagPro™ to the quadriceps muscle would have no influence on muscle endurance when exercising on a bicycle ergometer. Thus, the purpose of this study was to determine the efficacy of the topical product, MagPro™, because it relates to enhancing soft tissue flexibility and muscle endurance when used before implementation of these tasks.
Experimental Approach to the Problem
This was a double-blind, randomized, and controlled study. Both phases used a repeated-measures design. Although many components are involved in the performance of an athletic task, many of them are very challenging to quantify. Given that there was no literature on this product, a simplistic approach to a pair of quantifiable measures seemed to make the most sense. The quantifiable measures were flexibility and endurance. For phase 1, stretching of the gastroc-soleus complex was selected because of the ease of accessibility to application of the topical cream and the well-known standardized method of assessing gastroc-soleus flexibility. For phase 2, a bicycle ergometer provided an objective means of assessing muscle endurance. Resistance levels and revolutions per minute could be quantified and monitored. The quadriceps muscles were used because of their predominance in the cycling motion. Having each participant perform all components of the study with both creams served as the control for each condition.
All the participants were over 18 years of age and were recruited by a flyer or personal contact in a university community. Before data collection, each participant signed a consent form approved by the Institutional Review Board for the Protection of Human Subjects. Demographic data for the participants are displayed in Table 1. All the participants were healthy, physically active individuals but were not engaged in competitive athletics. Thus, the timing of being in-season or out-of-season was irrelevant. Nonetheless, exclusion criteria were clearly defined. The participants with sensory deficits or skin lesions (open wounds or rashes) in the lower extremities or a personal history of lower extremity surgery, cancer, diabetes mellitus, cardiovascular disease, or with the possibility of being pregnant were excluded. The participants with any lower extremity injuries in the past 6 months or with an allergy to a topically applied lotion were also excluded. The participants should not have been on any medication or receiving any treatment for muscle pathology.
Throughout the duration of the study, the participant, researcher #1, and researcher #2 were blinded to all treatment conditions rendered. Researcher #3 prepared the bottles of lotion used in the study. The MagPro™ cream bottle was labeled “A” and the placebo bottle was labeled “B.”
Once accepted into the study, each participant was positioned in long sitting on a plinth. Researcher #1 used a sharpie to mark 3 bony landmarks on each leg: fibular head, lateral malleolus, and head of the fifth metatarsal. Dorsiflexion of each ankle was measured by placing the axis of the goniometer on the lateral malleolus, the proximal arm in line with the fibular head and the distal arm in line with the head of the fifth metatarsal (19). This procedure is displayed in Figure 1. Researcher #1 presented the goniometer to researcher #2 to read and record the measurements (pretest) on the data collection form. A coin was flipped to determine the treatment rendered. If heads was flipped, the right calf was treated with the contents of bottle “A,” if tails was flipped, the left leg was treated with the contents of bottle “A.”
The participant was positioned prone for researcher #3 to apply the appropriate cream on the calf musculature. As per the manufacturer's recommendation, a 5-minute period of time was allowed for subcutaneous penetration of the cream. Then, the participant resumed the long-sit position to begin the stretching protocol. A 6-ft. long webbed strap was used for stretching of the calf muscles. The strap was placed under the ball of the foot and the 2 ends handed to the participant. The participant was instructed to pull on the strap until a strong sensation of tension or stretch was felt in the calf muscles (Figure 2). The participant was cautioned against the use of force beyond the pain threshold. The dorsiflexion stretch was held for 30 seconds and then followed by a 30-second rest period (2). After 5 stretches, ankle dorsiflexion was remeasured (midtest) by researcher #1 and recorded by researcher #2. A second set of 5 stretches was completed, and a final ankle dorsiflexion measurement (posttest) was performed. Throughout the process, researcher #4 was responsible for timing the stretching procedure. This entire protocol was repeated on the opposite calf with the other cream. The entire protocol took about 45 minutes.
As in phase 1, researchers #1 and #2 were blinded to all treatment conditions rendered. This time, a coin flip was used to determine the order of the treatment rendered (heads = cream “A”; tails = cream “B”). The appropriate cream (2 ml) was thoroughly rubbed into both the quadriceps muscles. The participant was positioned on the Life Fitness bicycle (a division of Brunswick Corporation, Schiller Park, IL, USA) with the foot on the pedal in the lowest position and the knee at 5° of flexion. The resistance was set to level 1, and the participant pedaled at least 50 rpm for 3 minutes. The resistance was increased by 1 level every 3 minutes. The exercise bout concluded when the participant could no longer maintain 50 rpm for 10 consecutive seconds. Although the amount of resistance that corresponds to each level of resistance to the Life Fitness bicycle is not known, the same bicycle was used for each participant to control for possible variations in resistance between pieces of equipment.
The entire protocol was repeated 24 hours later with the same cream. A minimum of 7 days later, at the same time of the day, the protocol was repeated with the other cream (2 bouts spaced 24 hours apart). In summary, the protocol was as follows: (a) day 1 = exercise 1 with cream A, (b) day 2 = exercise 2 with cream A, (c) day 8 = exercise 3 with cream B, and (d) day 9 = exercise 4 with cream B.
The maximum level of resistance obtained and total amount of time pedaled on the ergometer was recorded for each session.
To test hypothesis #1, an analysis of variance with repeated measures on time was performed on phase 1 (flexibility) data. In phase 1, the differences in the range of motion were compared for pretest to midtest, midtest to posttest, and pretest to posttest measurements of the MagPro™ and placebo creams. The purpose of serial measurements was to determine if 1 bout of five 30-second stretches produced significant results or if 2 bouts were needed. The intrarater reliability of the goniometric measurements was 0.87. Because all the measurements were taken by the same investigator, interrater reliability was not assessed. To test hypothesis #2, paired t-tests were performed on phase 2 (endurance) data to compare the total duration of both cycling bouts with the application of each cream. Thus, we sought to determine if endurance was greater on the second bout of exercise with each cream and if there was a difference in endurance between the 2 creams. Significance was set at the p ≤ 0.05 level for all analyses.
The results of phase 1 are displayed in Figure 3. There was no significant difference between the creams (p = 0.50), but there was a difference over time (p = 0.00). Post hoc analysis revealed a difference from pre to mid (p = 0.01), no difference from mid to post (p = 0.19), but an overall significant difference from pre to post (p = 0.00) measurements of ankle flexibility. The results of phase 2 are displayed in Figure 4. The statistical analysis did not reveal a significant difference between the first (p = 0.26) or second (p = 0.35) cycling bouts of either cream. Likewise, there were no differences between the first and second cycling bouts of the 2 creams (MagPro™ p = 0.46; Placebo p = 0.08). A power analysis for these data is displayed in Table 2.
There are numerous determinants of muscle performance. Mg2+ may be one of these components because it has a significant role in energy metabolism via basic mitochondrial functional, ATP transmembrane transport, muscle contraction or relaxation, membrane stability, and neuromuscular, cardiovascular, immune and hormonal functions (9,15). Approximately one-third of the total cellular Mg2+ is in the mitochondria (17,25). Mg2+ depletion has been reported to decrease antioxidant capacity, increase oxidative stress, and impair intracellular calcium homeostasis that result in swelling and structural damage to muscle cells (10,13,22). Depletion of Mg2+ may occur via reduced dietary intake (4) or physical exercise (14). Rayssiguier et al. (21) reported that lipolysis associated with endurance events might decrease plasma Mg2+ concentration. However, the marked decline in physical performance because of inefficiency in energy metabolism in animals does not correspond to the marginal deficiencies observed in humans (21).
Nuvialaet al. (20) examined the diets of 143 women (78 athletes; 65 sedentary) and found their Mg2+ intake to be 75.9–92.5% of the recommended daily allowance. Brilla and Haley (6) found that daily Mg2+ supplementation (up to 8 mg·kg−1) increased knee extension torque by 20% in young untrained individuals. Likewise, Brilla and Gunther (5) found improved endurance and reduced oxygen consumption during submaximal exercise after Mg2+ supplementation. Dominquez et al. (11) found Mg2+ levels correlated with improved grip strength, lower leg power, knee extension torque, and plantarflexion strength in older community dwelling adults (n = 1,453). In a study by Cinar et al. (8), 30 healthy men were divided into 3 groups (Mg2+ supplement, Mg2+ with exercise, and exercise). Glucose and insulin levels were assessed at the beginning and end of the 4-week study. Significant differences were noted in the glucose values of the supplemented groups, but there was no effect on insulin levels.
However, Weller et al. (24) found that 3 weeks of supplementation in athletes with low-normal serum Mg2+ did not improve performance and failed to increase the body's Mg2+ stores. Female athletes (n = 121) with a wide range of plasma Mg2+ levels were given supplements for 4 weeks. Although resting Mg2+ levels improved with supplementation, neither performance in nor recovery from physical activity was influenced (12). The lack of improvement in physical performance is consistent with the results of this study.
In testing hypothesis #1, topically applied MagPro™ cream did not improve gastroc-soleus flexibility. Although dorsiflexion range of motion of the ankle did improve for both types of creams after 5 bouts (MagPro™ = 3.33 ± 5.28; Placebo = 2.23 ± 4.82) and after 10 bouts of 30-second stretches (MagPro™ = 3.98 ± 5.27; Placebo = 4.47 ± 5.51), there was no statistically significant difference between the creams (p = 0.50). There was no condition-time interaction (p = 0.76) either.
In the testing of hypothesis #2, the MagPro™ cream did not enhance cycling endurance when applied to the quadriceps muscles. The duration pedaled was not any different from bout 1 (MagPro™ = 48.25 ± 6.60; Placebo = 47.67 ± 6.98) to that of bout 2 (MagPro™ = 48.29 ± 6.39; Placebo = 48.53 ± 6.69) of each cream. Nor was there a difference between the creams (p = 0.91).
Newhouse and Finstad (18) reported that Mg2+ is involved in 325 enzymatic reactions. Clearly, deficiencies could have many physiological effects. However, simple and inexpensive means of Mg2+ assessment has been a challenge (3,4,18). Although this study did not assess the Mg2+ levels of the participants to know if deficiencies existed, Bielinski (3) summarized the results on Mg2+ by saying that when plasma Mg2+ levels are within the normal range, supplements offer no significant benefits in terms of performance.
MagPro™ did not enhance gastroc-soleus flexibility over that of a placebo cream when using a standardized stretching protocol. MagPro™ also did not improve muscle endurance in initial or repeated exercise bouts on a bicycle ergometer. It is possible that there are other forms of exercise performances where Mg2+ supplementation may help. Perhaps, Mg2+ supplementation may enhance muscle strength. Repeated application of the MagPro™ cream after performance has been recommended by the manufacturer and may also influence performance. There are numerous other applications for which MagPro™ could be used and could be the scope of future studies. However, these factors were not studied here. What can be concluded from this study is that a single preactivity application of topical MagPro™ cream did not improve muscle flexibility or muscle endurance any more than a placebo cream did.
Custom Prescription Shoppe (Augusta, Georgia) provided the product for this study to be performed. However, Custom Prescription Shoppe did not have any involvement in the data collection, data analysis, or the writing of this manuscript. Thus, there is no conflict of interest to declare. The results of this study do not constitute endorsement of M MagPro™ by the authors or National Strength and Conditioning Association.
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