Muscle Power Clinical Trial
Official title:
The Effect of Vitamin D Supplementation on Muscle Power in Elite Cyclist
The purpose of this study is to evaluate the change in vitamin D status with the change in
muscular strength and muscular power in highly trained athletes over a 9-month study period.
The investigators hypothesize that the greatest muscular strength and power gains will be
demonstrated in the athletes who achieve and maintain a 25(OH)-D > 50 ng/mL (but < 100
ng/mL) over the 6 month study duration.
This hypothesis will be tested by carrying out the following specific aims: Aim 1. to
determine the extent to which increasing serum 25(OH)D to > 50 ng/mL is associated with
improved muscular power by assessing specific performance measures (e.g. Vertical Jump Test
and Wingate test) relative to lean body mass; and Aim 2. to examine the correlation between
vitamin D status and muscular power over time.
Study will be advertised through flyers at the training facilities and by word of mouth.
Researchers will schedule meeting with club members at the training facilities. At the
meetings, the researchers will give an explanation of the study and address any concerns or
questions that they may have. Cyclist will have an opportunity to sign up for participation
on a sign-up sheet or e-mail the PI directly to minimize any chance of coercion. Meetings
will take place in the training facilities in Tulsa, Oklahoma or the Oklahoma City
Metropolitan Area. At this time, subjects will complete an informed consent along with
demographic, anthropometric and health history, sunlight exposure, calcium and food
frequency questionnaires and PAR Q. All subjects will be asked to fill out the
questionnaires in the training facilities at various locations to ensure privacy. After
completion of the appropriate questionnaires, cyclist will be have venous blood from the
dominant arm (i.e., ~ 5 cc of blood) collected by a licensed medical professional and serum
samples stored for future analysis of vitamin D metabolites (i.e., 25-OH-vitamin D and
1,25-OH-vitamin D) and parathyroid hormone (PTH) concentrations. The cyclist's arm will be
cleaned with an alcohol swab, the blood will be drawn into a sterile vacutainer using a
sterile needle. At the completion of blood collection, the arm will again be cleaned using
sterile gauze and covered by a band aid to minimize the risk of infection. Samples will be
placed on ice in an ice chest until they are processed in the Nutritional Sciences
laboratories at Oklahoma State University. Subjects will then undergo skin tone analyses
followed by evaluation of specific performance measures of muscular strength and power.
These performance measures include: vertical jump test and a Wingate Power Test. All testing
and blood collection will take place at the training facilities.
Within 4 weeks of completing the baseline assessment, the investigators will meet with the
cyclist at their training facilities. Participants will be randomly assigned to placebo or
the vitamin D supplemented group. The vitamin D supplementation will consist of 100 mcg of
vitamin D/d, to be taken throughout the day. Participants will achieve 100 mcg by taking 2 x
25 mcg capsules per day. One will be taken at each time point (i.e., morning and evening)
throughout the day. Currently, there is no evidence suggesting that athletes require more
vitamin D then the general population for their age. Although we do not anticipate that the
dose of vitamin D used in this study, will produce intoxication (150 ng/mL), subjects who
exceed 100 ng/ml (i.e., upper end of the normal range) at any time will be asked to
discontinue the study. Studies that have demonstrated the benefits of vitamin D
supplementation on muscular strength and muscular power have combined vitamin D with
calcium. Therefore, all subjects (placebo and vitamin D supplemented group) will be given a
commercially available supplement of calcium and instructed to take with breakfast. The
calcium supplement is in the form of calcium citrate (500 mg per capsule).
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Allocation: Randomized, Endpoint Classification: Pharmacodynamics Study, Intervention Model: Parallel Assignment, Masking: Double Blind (Subject, Investigator, Outcomes Assessor), Primary Purpose: Basic Science
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