|The first December 2016 research update with studies that are relevant for both, women and men. I mean, who wouldn't want to get sign. more muscular in hours? I guess those who know that this is just an often overlooked measuring error.|
You're not interested in body fat data? Well, this is your lucky day. Today's installment of the short news will also discuss the latest study on the interaction between oral contraceptive and the adaptive response to exercise (Schaumberg. 2016).
That's still not for you? Well, there's also the interaction between glucose, fructose and gastric emptying, which is of "urgent" (keyword: diarrhea vs. fastest glucose uptake) importance for endurance athletes (Shi. 2016).
- Diarrhea vs. fastest glucose uptake - How the glucose / fructose ratio can make all the difference (Shi. 2016) -- In their latest study, scientists investigated the effect of beverage osmolalities, carbohydrate (CHO) type and CHO concentration on gastric emptying in euhydrated subjects at rest.
To this ends, the scientists measured the gastric emptying of water (W), and compared it to four glucose beverages containing either 2, 4, 6, or 8% glucose (2G, 4G, 6G, and 8G, respectively) and four sucrose (= 50% glucose + 50% fructose) beverages containing identical percentages, i.e. 2, 4, 6, or 8% of sucrose (2S, 4S, 6S, and 8S) in eight healthy subjects using the modified George double-sampling technique (Beckers. 1988).
Figure 1: Mean gastric residual volume and gastric emptying rate in with standardized drinks with different carbohydrate sources (glucose or sucrose = 1:1 glucose : fructose) and volume (Shi. 2016). Bad Fructose? Increased Glycogen Synthesis, Reduced Glycemia, Higher Glucose Oxidation | more
On the other hand, the risk of getting diarrhea may increase with each extra-gram of fructose in your intra- or post-workout beverage. The "optimal" 2:1 ratio for glycogen recompensation, I discussed in the previously cited article from 2013.
- Manipulation of Muscle Creatine and Glycogen Changes DXA Estimates of Body Composition (Bone. 2016) -- As the authors of the previously referred to study say dual x-ray absorptiometry (DXA) protocols are thought to provide a reliable measurement of body composition. In fact, however, their study shows that the accuracy will largely depend on the muscle glycogen content upon measurement (not so much on the level of creatine, though).
How do they know? Well, the researchers had eighteen well-trained male cyclists (the training status is important, because the results may well differ for untrained or only recreationally active subjects) participate in a parallel group application of creatine loading (n=9) (20 g/d for 5 d loading; 3 g/d maintenance) or placebo (n=9) with crossover application of glycogen loading (12 v 6 g/kg BM/d for 48 h) as part of a larger study involving a glycogen-depleting exercise protocol. Body composition, total body water, muscle glycogen and creatine content were assessed via DXA, bioelectrical impedance spectroscopy, and standard biopsy techniques.
Figure 2: Percent changes in leg lean and fat mass vs. baseline following glycogen depletion and creatine and glycogen loading with and without creatine (Bone. 2016).
- Oral Contraceptive Use Dampens Physiological Adaptations to Sprint Interval Training (Schaumberg. 2016) -- Dampens? Yes, this means "the pill" will impair your fitness gains - in this case maximal oxygen uptake (VO2peak) and peak cardiac output (Qpeak), but there is good news, too... before we get to that, however, we should take a brief look at the study design.
The scientists studied women taking oral contraceptives (OC | n=25) or experiencing natural regular menstrual cycles (MC; n=16) who completed an incremental exercise test to assess VO2peak, PPO, and Qpeak before, immediately after, and four weeks following 12 sessions of SIT. The SIT consisted of 10, one-minute efforts at 100-120% PPO in a 1:2 work:rest ratio.
Now, the bad news I've already revealed is that the OC group saw a significantly reduced increase in VO2peak (OC +8.5%; MC +13.0%; p=0.010) and Qpeak (OC +4.0%; MC +16.1%; p=0.013), but the good news is...
- the peak power output (PPO) increased to a similar extent in both groups (OC +13.1%; MC +13.8%; NS), and
- intriguingly, the OC group showed more sustained training effects in VO2peak (OC -4.0%; MC -7.7%; p=0.010) on the follow up 12 weeks later
Therefore, the authors conclusion that "OC use should be verified, controlled for, and considered when interpreting physiological adaptations to exercise training in women" (Schaumberg. 2016) is obviously right - during detraining, on the other hand, it could be an advantage to be on oral contraceptives (needless to say that the adaptation conserving effects would have to be proven in a future study in which MC women would be put on OC after SIT).
- Beckers, E. J., et al. "Determination of total gastric volume, gastric secretion and residual meal using the double sampling technique of George." Gut 29.12 (1988): 1725-1729.
- Bone, et al. "Manipulation of Muscle Creatine and Glycogen Changes DXA Estimates of Body Composition." Medicine & Science in Sports & Exercise: Post Acceptance: November 28, 2016 - doi: 10.1249/MSS.0000000000001174.
- Schaumberg, et al. "Oral Contraceptive Use Dampens Physiological Adaptations to Sprint Interval Training." Medicine & Science in Sports & Exercise: Post Acceptance: November 28, 2016 - doi: 10.1249/MSS.0000000000001171.
- Shi et al. "Effect of Different Osmolalities, CHO Types, and [CHO] on Gastric Emptying in Humans." Medicine & Science in Sports & Exercise: Post Acceptance: November 28, 2016 -doi: 10.1249/MSS.0000000000001176.