Is It Safe to Train When the Air Is Full of Wildfire Smoke?

Episode Overview

• Hosts Dr. Jordan Feigenbaum and Dr. Austin Baraki present a free preview of The Direct Line (a monthly Q&A for Barbell Medicine Plus subscribers, which costs $9.95/month with a $1/month trial), and also mention launching a book titled Signal alongside sponsors Ten Thousand, ButcherBox, Factor, Quince, and FIGS.
• The first half of the episode investigates the physiological impact of exercising in wildfire smoke and air pollution (PM2.5 and AQI), analyzing whether there is a tipping point where working out causes net harm and how indoor lifting compares to outdoor cardio.
• The second half addresses resistance training programming, specifically how to reconcile the "effective reps" model (the claim that only sets taken within 5 reps in reserve [RIR] build muscle) with the concept of "fractional sets" (counting secondary muscle involvement in compound lifts as 0.5 sets).
• Across both topics, the doctors emphasize that consistency and total cumulative work over months and years far outweigh environmental obstacles or the minutiae of set-by-set effort calculations.

Key Concepts

• Air Quality Metrics (PM2.5, AQI, and NowCast): PM2.5 refers to particulate matter smaller than 2.5 microns across—small enough to bypass the nose and throat, enter deep airways, and potentially enter the bloodstream. While a clean day sees PM2.5 in the single digits (around 5 $\mu\text{g/m}^3$), wildfire smoke can push levels to 100 or past 150 $\mu\text{g/m}^3$. The Air Quality Index (AQI) converts pollutant concentrations into a 0 to 500 scale based on 24-hour averages ($<50$ is green/good; 50–100 is yellow/moderate). Weather apps often use "NowCast," which weights the last few hours and can read meaningfully lower than real-time spikes when smoke is actively rolling in.
• Pathophysiology of Wildfire Smoke vs. City Pollution: Wildfire smoke consists mostly of organic material, contrasting with inorganic mineral dusts (like sandblasting) that cause fibrosing lung diseases (pneumoconioses). However, wildfire smoke is uniquely irritating; a Scripps study of 1.6 million respiratory-based hospital admissions found that while city particulate matter raised admissions by $<1.5\%$ per 10 $\mu\text{g/m}^3$ exposure, wildfire smoke raised admissions anywhere from 1.3% up to 10% per 10 $\mu\text{g/m}^3$. Short-term risks (acute reactive bronchospasm, hypersensitivity pneumonitis, hospital admissions, or needing prednisone/inhalers) are highest in vulnerable populations with pre-existing heart or lung disease (COPD, emphysema, chronic bronchitis, asthma), whereas long-term carcinogenesis requires high cumulative exposure over long periods.
• The Exercise Tipping Point in Polluted Air: While a 2016 modeling paper by Tainio predicted that cycling for 90 minutes a day at 100 $\mu\text{g/m}^3$ is the tipping point where harm outweighs benefit, Dr. Feigenbaum notes this was a theoretical model of city commuting with internal inconsistencies in the text (stating 1.5 hours in the abstract, 1 hour 15 minutes in the discussion, and "just more than an hour" in a follow-up review). More recent empirical data from a BMC Medicine pooled analysis of 7 cohorts (~1.5 million adults over a median 12-year follow-up, though heavily weighted toward two Taiwanese cohorts) showed that below a 25 $\mu\text{g/m}^3$ annual average (AQI ~80, comparable to Los Angeles), meeting exercise guidelines cut all-cause mortality by ~30%. Above 25 $\mu\text{g/m}^3$, the mortality benefit roughly halved to 12%–15%, and exercise remained protective all the way up to 50 $\mu\text{g/m}^3$ (AQI 137). Furthermore, a 6-city modeling study (Helsinki, London, São Paulo, Warsaw, Beijing, New Delhi) found that restricting active commuting on high-pollution days did not lower mortality anywhere, and actually increased modeled mortality in Beijing and New Delhi due to lost physical activity.
• Minute Ventilation and Indoor Filtration: The dose of inhaled particulates depends heavily on minute ventilation (breathing rate). Rest requires ~10 liters/minute of air, walking takes 23 L/min, and cycling jumps to 43 L/min. Lifting weights is much closer to walking than cycling; in one study of healthy individuals and COPD patients performing sets of 10 leg extensions, doubling the load from 40% 1RM to 80% 1RM increased perceived effort but did not increase breathing rate (though Dr. Feigenbaum caveats this was a single snapshot using leg extensions, not high-rep circuits). Meanwhile, an analysis of over 1,000 buildings during California wildfires showed that even indoors with filtration, indoor particulate matter nearly tripled, meaning staying inside does not completely eliminate exposure.
• Proximity to Failure (RIR) and the "Effective Reps" Fallacy: Reps in Reserve (RIR) estimates how many more reps you could perform at the end of a set (0 RIR is failure). Popular rhetoric often claims a "hard set" must be taken to $\le 5$ RIR to count for muscle growth. However, a 2024 meta-regression by the Data Driven Strength group and Zourdos (analyzing 140 results from 26 studies on muscle growth) found that the best fit for hypertrophy is a continuous straight line from failure all the way out past 20 RIR. Going from 5 RIR to 0 RIR yields a tiny benefit of ~0.1 standardized units, and head-to-head comparisons of failure vs. non-failure show a difference of 0.1 to 0.2 standardized units with a confidence interval that crosses zero (meaning zero difference cannot be ruled out). Thus, hypertrophy is a continuous gradient where even warm-ups and sets $>5$ RIR provide a non-zero stimulus.
• Fractional Sets for Secondary Muscles: To determine how much secondary "helper" muscles grow during compound lifts (e.g., biceps during chin-ups or triceps during bench press), a meta-analysis of 57 studies (~2,000 participants) tested counting indirect sets as 1, 0.5, or 0 sets. Counting indirect work as 0.5 sets fit the hypertrophy data best, proving that secondary muscles receive a meaningful, non-zero growth stimulus even if they aren't the primary limiting factor taken to failure.
• Internal Load and Individual Variation: Unlike endurance training, which can pair external work (pace/power) with objective internal load metrics (heart rate), resistance training lacks an objective mathematical formula for internal load, forcing lifters to rely on subjective RPE/RIR. Because inter-individual variation in training response is massive, and missing just 10 workouts or 30 sets over a year due to life events completely dwarfs the micro-differences between 3, 4, or 5 RIR, obsessing over exact proximity to failure is unproductive.

Quotes

• At 8:56 - "Yeah, I mean, the lungs are essentially exposed to the environment, you know, in the same way that our skin and our GI tract are organs that are essentially wide open to the external environment, our lungs are as well. So it's no coincidence that they are a frequent site of pathology, of infection, of inflammation. There's tons of immune activity happening in the lungs." - Dr. Baraki explaining the anatomical vulnerability of the respiratory system to inhaled particulates.
• At 10:11 - "Well, the best evidence we have here is that this, we'll call it dirty air, blunts the benefits of exercise, but we can't really see a point where, or a tipping point where it erases it. And the AQI, Air Quality Index, of 80 is where the benefit roughly halves. We just don't have any evidence that exercise ever becomes harmful in a particular environment." - Dr. Feigenbaum summarizing the BMC Medicine cohort data on exercising in polluted air.
• At 16:31 - "So your options are like be inside and don't exercise, or be inside and exercise. In which case, the being inside and exercise is, in my mind, more likely to benefit you than staying inside to avoid the particulate matter and then not exercising out of fear of some detrimental effect, which is, again, most likely outweighed by the benefits in that situation." - Dr. Baraki weighing the trade-offs of working out indoors during wildfire events when indoor PM2.5 is elevated.
• At 18:51 - "Taking a week off of exercise for this reason, whether for the wildfire reason or for some other reason, could evolve into two weeks off, four weeks off, six months later, they're like, 'Well, I took this one week off because of the wildfire and then I kind of lost momentum and I, you know, here we are six months or a year later and I haven't been able to get back to it.'" - Dr. Baraki highlighting the clinical and behavioral danger of breaking exercise habits during temporary environmental disruptions.
• At 28:30 - "My position on this overall, which I think I've stated a few times: any hardline sort of interpretation of effective reps, the effective reps model, is wrong. Meaning like, you got to take every set to five repetitions in reserve or closer, otherwise it doesn't count. That's a hardline version. The way I see this, it's more of a gradient, particularly for hypertrophy." - Dr. Feigenbaum refuting binary thresholds for muscle growth based on recent meta-regression data.
• At 36:31 - "And the main reason is that I feel that the differences in inter-individual response to training dwarf the differences in impact of any one or combination of these decisions. Such that the more practical strategy is just pick something, do it consistently for a while, see what happens, and iterate on that." - Dr. Baraki explaining why practical consistency beats perfectionism in programming RIR and volume.
• At 39:13 - "Over the course of a year, you miss a total of 10 training sessions for whatever reason. I think you missing 10 training sessions probably outweighs you agonizing over those types of things. Or you skip, you know, a total of like 30 sets across the whole training year. I suspect that that also outweighs, you know, the difference of whether I did one extra rep on these sets and took it an extra rep close to failure or not." - Dr. Baraki contextualizing how annual training adherence impacts results far more than single-rep effort adjustments.

Takeaways

• Modify, Don't Skip, Workouts During Wildfire Smoke: Unless you have pre-existing heart or lung disease (like asthma or COPD), do not skip exercise due to smoky air, as losing momentum can easily snowball into months of inactivity. Instead, move your training indoors with air filtration and favor resistance training over high-ventilation cardio to keep your breathing rate—and total inhaled particulate dose—low.
• Separate Your Effort Targets for Strength vs. Hypertrophy: For maximal strength, use loads around 60%–70% of your 1RM or higher and stay further from failure (RPE 4–6 or 4–7, which is 3–6 RIR) to preserve bar speed and force production. For muscle growth, aim for an "RPE sweet spot" of 7–9 (1–3 RIR), particularly on low-stakes isolation, machine, and dumbbell exercises, to balance stimulus against recovery costs.
• Count Indirect Compound Work as 0.5 Sets When Programming: When tallying weekly volume for smaller or secondary muscle groups (such as triceps in pressing or biceps in pulling), count compound lifts as half a set (0.5) toward your volume goals rather than ignoring them or counting them as a full set.
• Use Ascending Sets and Periodic "Re-Anchoring Weeks" to Calibrate RIR: Because people are worse at estimating RIR the further they are from failure, use ascending warm-up/working sets in Week 1 of a block (e.g., sets of 4 at RPE 7, 8, and 9) to find your bearings, and consider inserting a "re-anchoring week" every 5th to 7th week where you safely push machine or dumbbell exercises close to or to failure to recalibrate your internal gauge (keeping in mind Dr. Feigenbaum's caveat that this is a practical coaching hedge rather than a practice backed by hard data).