Welcome to my weekly summary of the latest research from the world of sports science!
Fueling mistakes are still common in endurance sports. These three studies examine whether the timing of carbohydrate intake affects performance or gut comfort, whether sodium bicarbonate meaningfully improves running performance, and how much strength training can deplete muscle glycogen in endurance athletes—read on.
Total Carb Intake Matters More Than Perfect Timing
This study examined whether the timing of carbohydrate intake during exercise affects performance and gastrointestinal comfort. Twelve trained male cyclists completed three randomized trials involving 180 minutes of intermittent cycling followed by a 15-minute all-out test and a sprint to exhaustion. Participants consumed 90 g/hour of carbohydrates in either an increasing pattern (starting low and finishing high), a decreasing pattern (starting high and finishing low), or a constant even pattern. The distribution of carbohydrate intake had no effect on performance in either test. However, the decreasing pattern resulted in slightly higher carbohydrate oxidation rates and better gut comfort later in exercise. Conversely, the increasing pattern led to more nausea, stomach fullness, and abdominal cramping over time compared to the decreasing pattern.
My thoughts: The authors of this study glaze over some very practical aspects of this work. One big takeaway for me is that if you are generally sensitive to gels on rides, front-load them and reduce your intake as you progress. You'll get the same benefit but reduce stomach issues. The key message remains that total carbohydrate intake matters far more than timing—aim for 90 g/hour during long efforts and distribute it in whatever pattern works for your gut. For most athletes, even intake every 15–20 minutes is still the safest and simplest approach, but if race conditions make that difficult, don't stress about perfect distribution.
Sodium Bicarbonate Shows Minimal Benefits for Running
This review examined whether a single dose of sodium bicarbonate improves continuous running performance. Across 11 placebo-controlled trials involving 126 participants, athletes typically consumed 0.3 g/kg about 90 minutes before runs lasting up to 30 minutes. Bicarbonate initially showed a small performance benefit; however, after accounting for gastrointestinal dropouts and publication bias, the effect was negligible and no longer statistically significant. Gastrointestinal side effects were common, occurring in about 30% of bicarbonate trials compared with roughly 3% of placebo trials, and nearly 9% of participants could not tolerate the supplement. Greater benefits were associated with male sex and higher body mass, and in male-only studies the performance effect remained small but statistically significant.
My thoughts: This is the kind of thing we're now seeing in research now that male and female athlete differences are being focused on. The big picture here is that for most runners in mixed populations, the performance benefit is tiny once you account for the real-world problems—mainly that roughly 1 in 3 people will experience GI distress and about 1 in 11 won't tolerate it at all. If you're an athlete willing to test your tolerance during training, there might be a small benefit, but the juice probably isn't worth the squeeze for most people, especially considering the GI lottery you're playing on race day.
Strength Training Depletes Glycogen in Endurance Athletes
This review looked at how resistance training affects muscle glycogen, the main stored fuel for exercise. Across multiple studies, strength training caused a meaningful drop in muscle glycogen—more than many athletes might expect—especially during longer workouts with more sets. Untrained individuals experienced greater glycogen loss than trained athletes, likely due to lower efficiency and conditioning. While typical lifting sessions don’t usually drain glycogen enough to hurt performance right away, the findings highlight that strength training does rely heavily on carbohydrates, particularly for high-volume or repeated sessions, making proper fueling important for recovery and ongoing performance.
My thoughts: Strength training is becoming more prominent with runners and cyclists, and for good reason. Through my interest in the physiology of HYROX and CrossFit athletes, I've seen firsthand how a shift to higher intensities blows through your body's carb stores, so this isn't a surprise. It does mean that the endurance folks need to pay closer attention to recovery than most, though. Add carbs to your post-strength session protein shake please. Don't just rely on protein alone—your muscles need to replenish glycogen stores after lifting, especially if you're doing endurance work the next day.
That’s all for this week! If you learned something new and are curious to know more, head over to the Blonyx Blog or my growing list of weekly research summaries where I help you further improve your athletic performance by keeping you up to date on the latest findings from the world of sports science.
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