RUN LONG, RUN HEALTHY — JULY 9, 2026

Can Cycling Replace Some of Your Running?

Plus — jumping for bone health during underfueling; vitamin D status and athlete lipid profiles; zero-drop shoes and running economy; carb mouth rinsing; and why motivation shapes how much you run

Just tasting carbs makes hard efforts feel easier

Carbohydrates are usually framed as fuel. You eat or drink them, they get absorbed, they help maintain blood glucose and carbohydrate availability, and you perform better.

But carbohydrates can also act before they become fuel.

A recent randomized trial tested carbohydrate mouth rinsing against music listening and a placebo mouth rinse during a hard 4-kilometer cycling time trial.

Eleven trained cyclists completed all three conditions. In the carbohydrate condition, they rinsed with a 6.4% maltodextrin solution — five 25 mL rinses, each swished for 10 seconds and spat out. The researchers measured prefrontal cortex oxygenation (essentially how much oxygen is in this particular brain region), executive function, perceived exertion every 500 meters, time-trial performance, heart rate, and blood lactate.

• The carbohydrate rinse increased oxygenation in both sides of the prefrontal cortex after the intervention and after the time trial compared with music and placebo.
• Executive function was also better after the time trial in the carbohydrate condition.
• Perceived exertion was lower with carbohydrate mouth rinsing than placebo at every distance interval, and lower than music through the middle of the trial.
• Performance improved modestly: completion time averaged 336.64 seconds with carbohydrate mouth rinsing versus 339.36 seconds with placebo and 339.43 seconds with music.
• Heart rate and lactate did not differ between conditions.

What this means for runners

For short, hard efforts — 5ks, final surges, hill reps, hard track sessions, or moments when your stomach does not want more fuel — carbohydrate mouth rinsing is a low-risk tool worth testing. It should not replace actual carbohydrate intake in longer races where fueling matters metabolically. But as a perceptual tool, especially late in a hard effort, swishing a carb drink and spitting or swallowing, depending on the context, may help reduce effort just enough to hold pace. Treat it like you would any race strategy: practice it before race day.

Can cycling replace some of your running?

Every runner eventually has to negotiate with impact.

That is where cycling becomes tempting. You can work hard, accumulate a lot of aerobic volume, and wake up the next day without the same “musculoskeletal hangover.” The question is whether that fitness actually transfers back to running.

A new systematic review and meta-analysis looked at exactly this question: Does training on the bike improve or maintain running-related fitness and performance compared with running itself?

The researchers included seven randomized controlled trials lasting at least four weeks, comparing running-only, cycling-only, or combined run-bike training in recreationally active, trained, or competitive participants. Outcomes included VO2 max measured on a treadmill, VO2 max measured on a bike, and running performance over 1 mile, 3,000 meters, or 5,000 meters.

• There were no statistically significant differences between running-only and cycling-only training for treadmill VO2 max, cycling VO2 max, or running performance.
• Run-only training favored treadmill VO2 max.
• Cycling-only training favored cycling VO2 max.
• For running performance, the effect between training modalities was essentially zero.

That sounds like a win for cross-training. But the nuance matters.

The review does not prove cycling is interchangeable with running. The authors are careful to note that the evidence base was small, many protocols were old, and several studies had some concerns regarding their methods. The more accurate interpretation is that, within the available evidence, researchers did not detect clear differences over short-to-moderate training periods between running and cycling.

What this means for runners

I’d treat cycling as one of the best tools runners have for increasing aerobic work while controlling orthopedic load, especially when the alternative is forcing more easy mileage into already tired legs. But I would not use it as a full substitute for the key running-specific pieces that make you race well, including long runs, race-pace work, strides, hills, and enough weekly running to keep your tissues prepared for impact. The practical move is to swap cycling for some easy or recovery volume, not for every run that teaches your body how to run fast, long, and efficiently.

Can jumping protect your bones when you’re underfueling?

Runners love to think about trade-offs. If we are not eating enough, maybe strength training protects us. If we are in a deficit, maybe impact loading keeps bones stimulated.

A new study tested a version of that logic, and the result is a useful warning for all runners.

Researchers studied 12 recreational female runners in a randomized crossover design. Each runner completed two five-day periods of controlled low energy availability, set at 15 calories/kg fat-free mass per day. That is low. The deficit came from both dietary restriction and daily treadmill running at 65–70% VO2 max. In one condition, participants only ran. In the other, they also completed 50 supervised depth jumps per day, separated from the run by at least four hours.

The idea was reasonable. Bone responds to mechanical loading, and previous work suggests that brief high-impact jumping might blunt some of the negative bone-marker changes seen during short-term underfueling. But here, when the jumping was layered on top of daily running and controlled low energy availability, it did not rescue bone turnover; in fact, it pushed bone metabolism in a direction consistent with bone breakdown.

• The bone resorption marker beta-CTX increased over time in both conditions.
• Bone formation markers, including P1NP and sclerostin, did not significantly change over time or differ between conditions.

The study was small and short, and it measured bone markers rather than long-term changes in bone mineral density or stress fracture risk. It also studied young female recreational runners without current low energy availability risk, hormonal contraceptive use, recent bone injury, or low bone density. So we should not overgeneralize. But the direction of the finding is hard to ignore.

What this means for runners

If you are underfueling, your bones may start showing unfavorable metabolic signals within days, not months. And no amount of jumping or plyometrics will help. The more practical approach is to treat energy availability as the foundation: eat enough total calories, enough carbohydrates around training, adequate calcium and vitamin D, and include recovery days that are actually recovery days. Jump training can be useful for bone and tendon health, but it works best when the body has the resources to adapt to it.

Can vitamin D status inform us about athlete cardiovascular health?

Vitamin D usually gets talked about in runner circles through the lens of bone health, immune function, and maybe muscle function. A new study looked at a different angle: whether vitamin D status is associated with a more or less favorable lipid profile in elite athletes.

The researchers analyzed 773 male professional athletes from German team sports, including handball, basketball, ice hockey, and soccer. The athletes were young, healthy, highly trained, and not taking regular medications. They also weren’t runners, but I still think we can learn something here.

They measured serum 25-hydroxyvitamin D and lipid markers, including LDL cholesterol, HDL cholesterol, triglycerides, and lipoprotein(a).

• Athletes with vitamin D levels at or above 30 ng/mL had lower LDL cholesterol than those below 30 ng/mL: 95 vs. 101 mg/dL.
• They also had lower triglycerides: 96 vs. 105 mg/dL.
• Lipoprotein(a) differed as well, with lower values in the vitamin D-sufficient group.
• Athletes with sufficient vitamin D also had higher peak exercise performance during a cycling test: 4.29 vs. 3.36 Watts per kilogram.

This was cross-sectional. It does not prove that vitamin D lowered LDL, triglycerides, or lipoprotein(a), and it definitely does not prove that taking vitamin D will improve cycling watts per kilogram. Higher vitamin D may be a marker of other things: more outdoor training, better nutrition, seasonal timing, healthier overall physiology, or sport-specific differences. The authors adjusted for a lot, but observational data cannot fully solve this.

What this means for runners

I would not read this as a reason to megadose vitamin D to chase lower LDL or Lp(a). That is not what the study tested. But I would read it as another reason to know your vitamin D status, especially if you train indoors, live far from the equator, avoid sun exposure, have a history of stress injuries, or get bloodwork showing low levels in winter. For runners, vitamin D is still most practically relevant for bone and general health. Any lipid connection is interesting, but for now, it is a signal to monitor, not a treatment strategy.

Zero-drop shoes improve running economy

Heel-toe drop is one of those shoe features that gets discussed constantly, but it is hard to isolate in real-world shoes among all of the other fancy foams and plates.

So a new study did something clever to specifically test how heel-to-toe drop influences running economy: it built custom shoes that differed in heel-to-toe drop — 0, 10, 20, and 30 mm — while keeping the shoe model and mass fixed.

Twenty runners ran at ~8 mph in each shoe condition while researchers measured metabolic cost of running (i.e., running economy), ground reaction forces, joint mechanics, and leg muscle behavior using ultrasound.

• Higher heel-toe drop increased net metabolic power during running. Going from a 20 mm drop to a 0 mm drop reduced net metabolic power (lowered the energy cost of running) by 1.6%.
• In performance terms, that is not nothing. The authors note that a 1.6% economy improvement could theoretically translate into roughly 1–3 minutes over a marathon, though that extrapolation should be treated cautiously.
• Higher-drop shoes increased ankle plantarflexion and shortened the length of the calf muscle during ground contact. The researchers propose lower-drop shoes allowed the calf muscles to operate at longer, more economical lengths.
• Higher-drop shoes also increased peak and average knee movements, suggesting a shift in mechanical demand up the leg.

The authors recommend zero-drop shoes for recreational and high-caliber runners who want better economy. I would soften that recommendation.

The study is well-designed for isolating heel-toe drop, but it is still a lab study at one speed in custom shoes. The shoes were also created by adding cushioning to change drop, which may have changed underfoot stiffness. And, importantly, running economy is not the only thing that matters. Injury risk, comfort, calf/Achilles tolerance, terrain, fatigue, and shoe-superfoam interactions all matter too. The authors themselves note that the effect of heel-toe drop on injury risk remains unsettled.

What this means for runners

If you already tolerate lower-drop shoes well, this study gives a plausible reason they might feel efficient. If you have always run in 8–12 mm shoes, I would not suddenly switch all your mileage to zero drop because of one study. The more useful approach is gradual experimentation: try a slightly lower-drop shoe for short easy runs or controlled workouts, watch how your calves and Achilles respond, and judge the shoe by the combination of economy, comfort, and durability in your own body.

Why you run may shape how much you run

Runners talk about discipline and consistency as if they were mostly a character trait. Some people have it; others do not.

But a new study suggests consistency may depend partly on the quality of your motivation.

Researchers analyzed 2,278 runners from the Garmin-RUNSAFE Running Health Study. Participants completed the BREQ-3 questionnaire, which assesses different types of exercise motivation along the self-determination theory continuum: from amotivation to external pressure to more autonomous forms like identified, integrated, and intrinsic motivation. The researchers then compared these motivation profiles with GPS-derived running data from the previous four weeks.

They identified four profiles.

• “Autonomous achievers” made up the largest group, at 1,379 runners, or 60.5% of the sample. These runners had high identified, integrated, and intrinsic motivation with low controlled motivation.
• “Balanced engagers” made up 620 runners.
• “Reluctant runners” were the smallest group, at 117 runners, with higher amotivation and lower autonomous motivation.
• “Controlled engagers,” at 162 runners, had moderate autonomous motivation but higher external and amotivated scores.

The training differences were meaningful. Autonomous achievers ran a median of 3.0 times per week, 161.5 minutes per week, and 17 miles/27 kilometers per week. Reluctant runners ran 1.5 times per week, 57.8 minutes per week, and 6 miles/9 kilometers per week. Controlled engagers and balanced engagers sat in the middle, with around 2.5 runs per week and about 12 miles/19 kilometers per week.

What this means for runners

You can’t wait until you feel perfectly motivated to go for a run or workout. The key is to build a training life that makes autonomous motivation more likely. Choose goals that actually matter to you, not just goals that look impressive online. Keep some runs social, some exploratory, and some performance-focused. Give yourself enough structure to progress, but enough flexibility that running still feels like something you get to do rather than something you are failing to keep up with. For coaches, this is a reminder that adherence is not just about prescribing the right mileage. It is about helping runners connect the work to values, identity, enjoyment, and ownership.

Thanks for reading. As always — Run Long, Run Healthy.

~Brady~