NUTRITION: Fructose-maltodextrin ratio in a carbohydrate-electrolyte solution differentially affects exogenous carbohydrate oxidation rate, gut comfort, and performance
Most of the sports drinks and gels I have used in the past have had a 2:1 maltodextrin:fructose ratio. This is based on the previous research that suggests there are limits to the rate at which glucose and fructose can be transported across the small intestine wall. The limits were thought to be ~60g/hr for glucose and ~30g/hr for fructose. However more recent research and practical trials have suggested that these limits may be exceeded.
In this study from 2011, the authors tested a range of ratios for maltodextrin to fructose. Their findings were that:
Relative to 0.5-Ratio [0.5 fructose to 1 maltodextrin], there were moderate improvements to peak power with 0.8- and 1.25-Ratio. Increases in stomach fullness, abdominal cramping, and nausea were lowest with the 0.8- followed by the 1.25-Ratio solution.
At high carbohydrate-ingestion rate, greater benefits to endurance performance may result from ingestion of 0.8- to 1.25-Ratio fructose-maltodextrin solutions. Small perceptible improvements in gut comfort favor the 0.8-Ratio and provide a clearer suggestion of mechanism than the relationship with exogenous carbohydrate oxidation.
PRACTICAL TAKEAWAY - higher ratios of fructose to glucose may be beneficial when consuming high rates of CHO during exercise.
This narrative review investigated the current research on the impact of performance from "five popular diet approaches: (a) vegetarian diets, (b) high-fat diets, (c) intermittent fasting diets, (d) gluten-free diet, and (e) low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diets". This is a fantastic paper and provides plenty of detail on the benefits and detriments of these different diets.
My notes and highlights includes:
Considering all findings from the review, all five diets discussed in detail appear to have both beneficial and detrimental effects on endurance performance.
For vegetarian diets, we suggest that when adjusting the athlete’s diet a sports dietitian is to (a) determine which vegetarian diet the athlete is consuming; (b) control the athlete’s micronutrients and related biomarkers, especially vitamin B12, folate, vitamin D and iron; (d) regulate the athlete’s energy needs and all macro and micronutrient needs to prevent any deficiency, and (c) monitor the diet consumption and adjust it according to the needs based on individual- and sports-specific needs.
Reviews of the HFD and sports performance have controversial results, the scientific evidence on the effectiveness of HFD on endurance performance is not strong enough to recommend these diets to endurance athletes.
Considering all the relevant study results, we can say that a low-FODMAP diet may benefit more from GFD unless athletes have celiac disease. However, it should be kept in mind that the implementation steps of the low-FODMAP diet are complex and require careful monitoring by a trained dietitian. In addition, only lactose and fructose elimination from the diet should be considered in endurance athletes prior to adopting a low-FODMAP diet.
PRACTICAL TAKEAWAY - there are benefits and detriments to all diets. Carefully consider your goals and how your diet can be aligned to best support those goals.
NUTRITION: Continuous Glucose Monitoring During a 100-km Race: A Case Study in an Elite Ultramarathon Runner
Continuous Glucose Monitoring (CGM) has become quite a popular topic in 2020 and 2021 with new devices available to help people measure themselves and using their phones. As a relatively new topic there isn't much information on how best to use CGMs to improve performance. This paper looked at two runners in a 100km run and analyzed their data to understand "the relationship between glucose profile and change in running speed".
The authors found that:
The average relative intensity throughout the 100-km race was 89.9% ± 5.8% lactate threshold (LT) in runner A and 78.4% ± 8.6% LT in runner B.
The total amount of carbohydrate intake during the race was 249 g and 366 g in runners A and B, respectively.
Despite lower carbohydrate intake, runner A maintained a normal glucose level throughout the race, while runner B rapidly decreased blood glucose and became hypoglycemic after the 80-km point.
These results suggest that elite ultramarathon runners may have the ability to prevent a large decrement in blood glucose level regardless of the amount of energy intake during the race to maintain higher relative running intensity.
PRACTICAL TAKEAWAY - there is still some work required to understand and interpret data from a CGM, especially during an ultramarathon.
TRAINING: The effects of recovery duration on physiological and perceptual responses of trained runners during four self-paced HIIT sessions
This study set out to determine the impact of the duration of recovery periods on running intervals. The protocol used was "participants performed a HIIT session comprising six 4-min work intervals, in which the recovery duration between work intervals equalled either a fixed (1MIN, 2MIN, 3MIN) or a self-selected duration (ssMIN)"
The authors found that:
Mean running velocity was significantly higher in 3MIN compared with all other protocols, and higher in ssMIN compared with 2MIN. No significant differences in time spent ≥90% and 95% V˙O2max, or ≥90% and 95% HRmax were evident between the four protocols.
Longer recovery durations may facilitate a higher external training load (faster running), whilst maintaining a similar internal training load (physiological stimulus), and may therefore allow for greater training adaptations.
PRACTICAL TAKEAWAY - alternating the duration of recovery in between intervals may impact the running speed, but has little impact on the total physiological training load of a session.
TRAINING: Maintaining Physical Performance: The Minimal Dose of Exercise Needed to Preserve Endurance and Strength Over Time
Understanding the detraining impact is important to plan off-season training and to manage annual training load. Additionally, during unexpected circumstances such as injury or the pandemic it is useful to understand the minimum dose required to maintain fitness.
This paper suggest that:
In general populations, endurance performance can be maintained for up to 15 weeks when training frequency is reduced to as little as 2 sessions per week or when exercise volume is reduced by 33-66% (as low as 13-26 minutes per session), as long as exercise intensity (exercising heart rate) is maintained.
Strength and muscle size (at least in younger populations) can be maintained for up to 32 weeks with as little as 1 session of strength training per week and 1 set per exercise, as long as exercise intensity (relative load) is maintained; whereas, in older populations, maintaining muscle size may require up to 2 sessions per week and 2-3 sets per exercise, while maintaining exercise intensity.
PRACTICAL TAKEAWAY - if you have to limit your training, try to maintain at least two endurance type sessions a week and one strength session a week to minimize the rate of detraining.
TRAINING: Is there an optimal training intensity for enhancing the maximal oxygen uptake of distance runners?
Improving VO2 Max is often a primary goal for many runners as this improves overall performance in races. This study set out to understand what the optimal training is to improve VO2 Max.
The minimum training intensity that elicits the enhancement of VO2 Max is highly dependent on the initial VO2 Max, however, and well trained distance runners probably need to train at relative high percentages of VO2 Max to elicit further increments.
Well trained distance runners have been reported to reach a plateau in VO2 Max enhancement; however, many studies have demonstrated that the V-dotO(2max) of well trained runners can be enhanced when training protocols known to elicit 95-100% VO2 Max are included in their training programmes.
PRACTICAL TAKEAWAY - while the starting VO2 Max of an athlete will dictate how much potential there is to increase this capacity, it appears that higher intensity intervals are needed with well-trained athletes to make any improvements.