Here’s your free but abridged version of this week’s “Run Long, Run Healthy” newsletter. Subscribe below to receive the complete, full-text edition with the newest and most authoritative scientific articles on training, nutrition, shoes, injury prevention, and motivation.
Can Sprinting Make You a Better Distance Runner?
Runners—we thrive on mileage. However, a new study indicates that you might be able to improve your performance by swapping distance for speed.
Researchers recruited 20 well-trained male distance runners (VO2 max ~67 mL/kg/min and a 5k personal best of ~14:38) and split them into two groups:
1. Sprint interval training (SIT) group: 10×30-second all-out sprints with 3.5 minutes of rest, twice per week for six weeks.
2. Traditional training group: Continued their usual long-distance training, also twice per week.
Outside of these sessions, both groups maintained their regular endurance-based training (40-60 minute jogs, four times per week).
After six weeks, the SIT group outperformed the traditional group in key endurance metrics: They had an improved time to exhaustion (a key indicator of endurance), a faster 3,000-meter time trial time (experiencing a ~5-second improvement versus no change in the traditional training group), and faster 100-meter and 400-meter times (suggesting better speed and neuromuscular efficiency).
Surprisingly, VO2 max didn’t improve significantly in either group, though SIT showed a small effect. However, running economy (oxygen cost) improved moderately in the SIT group, meaning they became more efficient runners.
What this means for your training
Sprint intervals aren’t just for sprinters. This study suggests well-trained endurance runners can gain real benefits by incorporating sprint work and adding 1-2 SIT sessions per week—I’d speculate that runners of all levels can experience something similar.
Now, this doesn’t mean you need to replicate the protocol in this study—even some short strides can help you be a better runner. However, all of us should probably sprint from time to time.
Use sprinting strategically during base training to improve performance without adding volume or to help develop your kick and running efficiency as your goal race approaches. And, of course, be sure to balance sprinting with easy running—this is an addition, not a replacement for quality mileage, which remains the staple of a well-rounding training plan whether you’re training for a 5K or a marathon.
RELATED ARTICLE: The 6 Best Sprint Workouts For Beginners To Help You Get Faster
🎙️ How to Follow this Weekend’s Tokyo Marathon + We Rank the World Major Marathons
🇯🇵 In our latest episode, Katelyn, Alex, and Michael break down everything you need to know about the upcoming Tokyo Marathon—from the elite field and course insights to the race’s rich history. 🏃♂️🔥
Plus, we shake things up with a power ranking of all six World Marathon Majors—where does Tokyo land? Watch or listen to find out! 🎙️
Smartwatches Predict Race Times with Surprising Accuracy (At Least the Short Ones)
Sometimes, our GPS watch predictions are insultingly slow, and other times, they’re laughably out of reach—vastly over- or underestimating what we could run for anything from a mile to the marathon. So, how accurate are those predictions? Do they actually reflect your fitness, or are they just estimates that fall apart on race day?
A new study put one smartwatch’s prediction algorithm to the test, comparing estimated race times to actual performances.
Researchers recruited 154 amateur runners (123 men, 31 women) who regularly trained and raced in distances from 5K to the half marathon. Each runner wore a smartwatch for at least six weeks, allowing the device to collect training data and refine its performance predictions.
Runners then completed actual race efforts over 5K, 10K, and 21.1K distances, with their smartwatch-predicted finish times recorded before each test.
Overall, the smartwatch’s predictions were within 3% of actual times in most cases, meaning an accuracy rate exceeding 97%. It was able to predict the runners’ 5K times within ~20 seconds and their 10K times within ~4 seconds. The prediction accuracy faltered as the distance increased—half marathon prediction times had an error of about 2.5 minutes.
What this means for your training
If you rely on your smartwatch for pacing guidance or goal setting, this study offers some useful insights. Your smartwatch is likely a good predictor of your race time—especially for 5K and 10K. If it says you’re in shape for a certain time, you can probably target that pace with confidence. However, because longer races introduce more variables—fueling, pacing, and fatigue all play a bigger role—performance predictions become less accurate.
RELATED ARTICLE: Marathon Pace Calculator: Plan Your Target Pace + Splits
How Men’s and Women’s Hearts Adapt Differently to Training
Resistance training (lifting weights) and endurance training lead to distinct adaptations that make our heart muscles stronger, more efficient, and in some cases physically larger. Until recently, however, it wasn’t known whether men and women respond differently to these two types of training—an important question because of the well-known sex differences in cardiac physiology and responses to exercise.
A new randomized crossover study tackled this question, examining how the heart’s structure and function change after 12 weeks of endurance vs. resistance training.
Researchers recruited 64 healthy but untrained individuals (38 women and 26 men). They randomized them to either 12 weeks of endurance training (running & cycling, 3x per week) or 12 weeks of resistance training (progressive strength workouts, 3x per week).
After a 12-week washout period, participants switched to the other training modality, allowing researchers to compare how the same individuals responded to both types of training.
Overall, endurance training led to healthier heart adaptations than resistance training. Resistance training in men led to thicker heart walls but worsened relaxation or diastolic function (potentially increasing stiffness). Endurance training improved the size of the heart’s chambers (specifically the left ventricle) and its ability to fill with blood (diastolic function) and pump blood (systolic function) efficiently.
Men’s hearts responded more to resistance training—left ventricle size increased significantly. Furthermore, after resistance training, men showed signs of worsened diastolic function—the heart became stiffer.
Women showed no significant cardiac changes after resistance training. Women’s hearts adapted more to endurance training. Left ventricle size increased in both men and women, but women showed better diastolic function improvements. Both sexes had no major changes in systolic function after endurance training.
What this means for runners and strength athletes
If you’re looking for cardiovascular improvements, endurance training improves heart structure and function without adding stiffness—especially for women.
While endurance training improves heart function, strength training still benefits musculoskeletal health and performance—that’s why we do both. For endurance athletes, prioritizing aerobic work while integrating strength training strategically may be the best approach for long-term cardiovascular health and performance.
RELATED ARTICLE: 8 Must-Do Marathon Strength Training Exercises for Runners
SHORT STUFF You Don’t Want To Miss
Clayton Young’s Road to Boston
Clayton Young—one of America’s best and newest marathon stars, is putting out some incredible content on YouTube detailing his training for various races. His latest installment—the Road to Boston—follows his training leading up to the 2025 Boston Marathon. I highly recommend watching while on the treadmill or when you need some extra motivation to train.
An interesting post: What type of runner are you?
This fun post on X sparks some self-reflection by asking runners to identify their “type” using four running books—The cult classic “Once a Runner,” “Born to Run” (which inspired the short-lived barefoot running revolution), Haruki Murakami’s “What I Talk about When I Talk about Running,” and “Never Finished” by David Goggins (Google him if you must).
I’m #1, by the way.
HERE’S WHAT ELSE YOU WOULD HAVE RECEIVED this week if you were a subscriber to the complete, full-text edition of “Run Long, Run Healthy.”
- The physiological demands of running on even vs. uneven surfaces
- CBD improves performance by reshaping the gut microbiome
- Which training approach is best—polarized or pyramidal training?
- Running influencers promoting Advil
- Should you take creatine?
Thanks for reading. As always—Run Long, Run Healthy
~Brady~
