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

Parts of the country now get a few weeks of wildfire smoke every year, and the obvious question is whether there is a point where the air is bad enough that the workout costs you more than it gives you. We went and looked. There is a real number, it comes from about 1.5 million people, and it is not the number that gets quoted.
This is a free preview of Direct Line, our monthly ask-us-anything for Barbell Medicine Plus subscribers. Two of this month's twelve questions are here in full.
First: training in wildfire smoke. What PM2.5 is, why the AQI on your phone and the number in the paper are not the same quantity, where the 90-minutes-at-100-micrograms figure comes from and why it is softer than it sounds, what happened when six cities modeled telling people to stay inside, and why your breathing rate during a set of squats matters more than you would think.
Second: the effective reps model. A subscriber noticed that if a set only counts when you are within five reps of failure, the triceps in a heavy bench press should not count, and if you are going to count that as a fractional set for the triceps, then a warm-up set counts for the chest. Both cannot be true. We go through the meta-regression on proximity to failure, the 67-study analysis that tested whether an indirect set should count as one, as half, or as zero, and where we actually put our sets.
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Timestamps
1:47 The question: is there a point where the air is too bad to train?
2:37 What PM2.5 actually is
3:05 AQI vs micrograms, and why your phone disagrees with the paper
3:50 Where the "90 minutes" number comes from
4:54 Austin: what breathing this air does to your lungs
9:14 1.5 million adults: does dirty air cancel the benefit of exercise?
10:44 Six cities modeled staying indoors. Mortality did not improve.
11:22 Lifting vs cycling: breathing rate is the whole mechanism
12:33 Indoor air during a wildfire, and what filtration does not fix
13:24 Is wildfire smoke worse than city pollution?
14:38 What we would actually tell a patient
18:35 The question: hard sets, fractional sets, and the five-rep rule
19:18 Reps in reserve, hard sets, and fractional sets defined
20:19 The meta-regression: no threshold, just a line
21:13 Do indirect sets count as half a set?
23:08 Would you rather: every set at 5 RIR, or every set to failure?
25:22 Why you get worse at judging RIR the further you are from failure
28:42 The numbers we use: RPE 7 to 9 for hypertrophy, 4 to 6 for strength
29:20 Austin: individual variation dwarfs all of this
33:28 Why nobody can measure training load in the weight room
Resources
Tainio M, de Nazelle AJ, Götschi T, et al. Can air pollution negate the health benefits of cycling and walking? Prev Med. 2016;87:233-236. doi:10.1016/j.ypmed.2016.02.002. PMID 27156248
Ku PW, Steptoe A, Hamer M, et al. Does ambient PM2.5 reduce the protective association of leisure-time physical activity with mortality? A systematic review, meta-analysis, and individual-level pooled analysis of cohort studies involving 1.5 million adults. BMC Med. 2025;23(1):647. doi:10.1186/s12916-025-04496-y. PMID 41310726
Giallouros G, Kouis P, Papatheodorou SI, Woodcock J, Tainio M. The long-term impact of restricting cycling and walking during high air pollution days on all-cause mortality: health impact assessment study. Environ Int. 2020;140:105679. doi:10.1016/j.envint.2020.105679. PMID 32353667
Sun S, Cao W, Qiu H, et al. Benefits of physical activity not affected by air pollution: a prospective cohort study. Int J Epidemiol. 2020;49(1):142-152. doi:10.1093/ije/dyz184. PMID 31504557
Robles P, Araujo T, Brooks D, et al. Cardiorespiratory responses to short bouts of resistance training exercises in individuals wi...