Research Update: 5000 IU/day Vitamin D, 12g/day Citrulline Malate or Barefoot Running What's the Most Ergogenic?

Who would have thought that barefoot running triggers instant improvements in running economy?

With the release of ahead of print articles for the next issue of the Journal of Strength and Conditioning Research, it is high time for yet another research update; an update with research on the effect of vitamin d supplementation on training adaptation in well trained soccer players, acute citrullin malate supplementation (10 grams 60 minutes before a workout) and high-intensity cycling performance, as well as information about the ability of barefoot running to reduce oxygen cost and improve running economy in female distance runners who have never run barefoot before.

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• The effect of vitamin d supplementation on training adaptation in well trained soccer players (Jastrzebska. 2016) - In view of the fact everybody appears to believe that the currently available evidence would imply that vitamin D supplements could enhance athletic performance, it is hardly surprising that the next issue of the Journal of Strength and Conditioning Research will contain yet another study investigating the effects of vitamin D supplements on athletic performance.
  
  What distinguishes the study at hand from the rest of the pack is that it was conducted in high-level, well trained athletes, who received either a placebo (PG) or 5000IU of vitamin D per day (SG). Both groups were subjected to the same "High Intensity Interval Training Program".
  

  

  Figure 1: Overview of he training regimen, the subjects were subjected to.

  The selection to the groups was based on peak power results attained before the experiment and position on the field. Blood samples for vitamin D level were taken from the players. In addition, total work, 5-10-20-30 m running speed, squat jump, and countermovement jump height were determined.
  
  Much to the disappointment of the average vitamin D enthusiast, there were no significant differences between SG and PG groups for any power-related characteristics at baseline. What did work, though, was the training: All power-related variables, except the 30 m sprint running time, improved significantly in response to interval training. However, the mean change scores (the differences between post- and pre-supplementation values) did not differ significantly between SG and PG groups. Thus, the authors of the study conclude that...

  

  Remember the differential effect of Vitamin D on breast cancer risk in lean vs. obese women?

  "[...] an 8-week vitamin D supplementation in highly trained football players was not beneficial in terms of response to high intensity interval training [and that, g]iven the current level of evidence, the recommendation to use vitamin D supplements in all athletes to improve performance or training gains would be premature" (Jastrzebska. 2016).

  What may make sense, however, is to avoid a seasonal decrease in 25(OH)D level or to obtain optimal vitamin D levels via higher dietary intakes and, optionally, vitamin D supplementation. Why that? Well, in vitamin D deficient athletes, there's at least some evidence that supplementing, or rather increasing the 25OHD levels help.
• Acute Citrulline-Malate supplementation and high-intensity cycling performance (Cunniffe. 2016) - Unlike the results of a previously discussed study on the effects of citrulline supplementation during an intense leg workout, in which 8g/day triggered significant performance increases, the recent double-blind, placebo-controlled, crossover study by Cunniffe et al. found no benefits of 12g of citrulline malate (in 400ml) compared to lemon sugar-free cordial (Placebo [PL]) when the 10 subjects consumed it 60 min prior to completion of two exercise trials... or, to be precise, only the heart rate differed significantly.
  

  

  Figure 2: Mean performance in the two groups; # sign. inter-group difference (p < 0.05 | Cunniffe. 2016)

  They consumed it 60 minutes before the workouts? Right, this happens to be the same protocol, Wax et al. used 2014 in 12 advanced resistance trained male subjects. What was different, however, is the type of exercise. While Wax et al. had their subjects squat and leg press, Cunniffe investigated the effects in a trial that consisted of ten (x 15 s) maximal cycle sprints (with 30 s rest intervals) followed by 5 min recovery before completing a cycle time-to-exhaustion test (TTE) at 100% of individual peak power (PP). I guess that explains the difference and suggest that the performance enhancing effects of citrulline are exercise dependent - obviously, this has to be investigated in future studies ;-)
• Barefoot running reduces the submaximal oxygen cost in female distance runners (Berrones. 2016) - The two most important ways to increase your running performance are (a) improving your VO2max, (b) improving your running economy aka the "O2 costs of running". That this can be achieved as easily as by dropping your shoes is thus a quite important result, Berrones et al. observed in during three 5-minute submaximal running trials representing 65, 75, and 85% of VO2max in fourteen recreationally active, trained distance female runners (age = 27.6 +/- 1.6 yrs; height = 163.3 +/- 1.7 cm; weight = 57.8 +/- 1.9 kg) who were completely inexperienced with unshod running.
  
  Following initial testing, each subject was randomized to either unshod or shod for days 2 and 3. Berrones et al. analyzed the data with a 2-way (condition by intensity) repeated measures ANOVA. The results of this analysis shows that the runners' submaximal oxygen consumption was significantly reduced at 85% of VO2max (P = 0.018), but not during the 65% or 75% trials (P > 0.05, both).
  

  

  The improvement in VO2 consumption during barefoot running was sign. only for 85% VO2max (Berrones. 2016).

  No other dependent measure, i.e. respiratory exchange ratio (RER), lactate, heart rate (HR), and ratings of perceived exertion (RPE), was different between unshod and shod conditions; and still, the scientists' conclusion that "training or competing while barefoot may be a useful strategy to improve endurance performance" (Berrones. 2016) may be useful for recreational or competitive distance runners.

You want more short exercise news? Well, this is not exactly a short one, but still: "GYM-Science Update: Bands Aid W/ Deadlifts? 16x1 or 4x4 for HIIT? Kettlebell HIIT Workout Better Than HIIT-Cycling?" | more

Bottom line? Well, I guess I should answer the question in the headline even if it is obvious, right? The answer is: "barefoot running". What we should not forget, though is the fact that previous research suggests that having normal (not extra-high) vitamin D levels is as important for athletes as 8g of citrulline are useful for strength trainees.

Against that background I wouldn't be surprised if the next SuppVersity Research Update featured studies showing beneficial effects of vitamin D and citrulline malate supplements and no or even ill effects of barefoot running... but hey, the results of the Berrones study are still impressive, right? Don't forget: the subjects had never run barefoot before | Comment on Facebook!

References:

• Berrones, Adam J.; Kurti, Stephanie; Kilsdonk, Korey; Cortez, Delonyx; Melo, Flavia; Whitehurst, Michael. "Barefoot running reduces the submaximal oxygen cost in female distance runners." Journal of Strength & Conditioning Research: Post Acceptance: January 19, 2016. doi: 10.1519/JSC.0000000000001330. 
• Cunniffe, Brian; Papageorgiou, Maria; O’Brien, Barbara; Davies, Nathan A; Grimble, George K; Cardinale, Marco. "Acute Citrulline-Malate supplementation and high-intensity cycling performance." Journal of Strength & Conditioning Research: Post Acceptance: January 19, 2016. doi: 10.1519/JSC.0000000000001338.
• Jastrzebska, Maria; Kaczmarczyk, Mariusz; Jastrzebski, Zbigniew. "The effect of vitamin d supplementation on training adaptation in well trained soccer players." Journal of Strength & Conditioning Research: Post Acceptance: January 20, 2016. doi: 10.1519/JSC.0000000000001337
• Wax, Benjamin, et al. "Effects of Supplemental Citrulline Malate Ingestion During Repeated Bouts of Lower-body Exercise in Advanced Weight Lifters." The Journal of Strength & Conditioning Research (2014).