A two-a-day is two training sessions in one day. People end up there for three reasons: an athlete's schedule, a day with two short gaps instead of one long one, or wanting to keep lifting and cardio apart. All three ask the same question: does splitting the day help, hurt, or make no difference?
This page is what the trials measured, which is strength and muscle, not health or recovery in general. How many days a week to train is a different question, and how often to train is the page for it. This one is about the sessions inside a single day.
What the two-a-day trials found
Three trials compared one session a day with two. All three are small and short, and all three studied trained people or athletes.
| Trial | Who | Design | What happened |
|---|---|---|---|
| Häkkinen and Kallinen, 1994 | 10 female athletes | Three weeks of one daily session, then three weeks with the same total volume split into two daily sessions | No systematic change in strength or quadriceps size over the one-session period; significant gains in both over the two-session period1 |
| Hartman and colleagues, 2007 | 10 nationally competitive male weightlifters, about 20 years old | Three weeks, similar volume, once or twice a day | No significant differences between the groups on any measure2 |
| Corrêa and colleagues, 2022 | 23 resistance-trained men | Eight weeks, each muscle group trained once or twice a day | Squat one-rep max rose 16.1 percent with two daily sessions and 7.8 percent with one; bench press, muscular endurance and muscle thickness rose in both, with no difference between them3 |
Read together: two sessions a day never did worse than one in these trials, and twice it did better on a strength measure. Hartman's group concluded there were no additional benefits from training twice a day in national-level weightlifters.2 Corrêa's group concluded the extra daily session helped lower-body strength but did not add to upper-body strength, muscular endurance or muscle growth.3 A design note on the 1994 trial: its two periods ran one after the other in the same athletes, so the two-session period also came second.
Why the split might help strength but not size
Two larger bodies of research line up with those results, and the line is a hypothesis, not a finding of the two-a-day trials themselves. For muscle growth, a meta-analysis of 25 studies found that when total volume was matched, how often a muscle was trained made no meaningful difference.4 For strength, a 2026 meta-regression of 67 studies found strength gains increased with training frequency, with diminishing returns, while frequency's effect on muscle growth was compatible with a negligible one.5 That's the same pattern as the 2022 trial: more strength, similar size. Häkkinen's own reading was that smaller units of training may give the nervous system a more effective stimulus.1
Lifting and cardio on the same day
This is the two-a-day most people actually do. In a seven-week trial of 58 amateur rugby players, three of the groups did strength and aerobic training with 0, 6 or 24 hours between them; strength gains in the bench press and half squat were lower with no gap than with 6 or 24 hours, and the authors advised against scheduling the two with less than six hours of recovery between them.6 They also found twice a day with a six-hour gap was, to a lesser extent, not optimal compared with a full day apart.6 The larger picture points a different way: a 2022 meta-analysis of 43 studies found adding aerobic training did not compromise muscle growth or maximal strength, and found explosive strength took a bigger hit when the two shared a session than when they were at least three hours apart.7 So the six-hour gap is one trial's advice for athletes, and a few hours apart is a reasonable practical floor.
If they have to share one session, lift first: a 2018 meta-analysis found lower-body strength was higher when strength training came before endurance training in the same session, and the order made no difference to aerobic capacity.8 Cardio and lifting together has the rest of that research.
How to set up a two-a-day (practical)
Two of the trials split the same training rather than adding to it. So the rule is: take one day's work and divide it, keeping the weekly sets the same. The set-ups below are practical, not tested as written.
| Why two sessions | Morning | Evening |
|---|---|---|
| Two short gaps in the day | The first half of the session: the main lower and upper lifts | The second half: the second pair and the small muscles |
| Lifting and cardio apart | The lifting session | The cardio, six hours later or more where the day allows |
| A split by body part | Lower body | Upper body |
Keep the weekly sets inside the ranges on how many sets per week, and keep the days off: two-a-days don't replace rest days. Write the weights down; if the evening session's weights keep dropping below the morning's plan, the day is too full. A full single session with time to spare is on the 1-hour workout plan.
Common questions
Is it bad to work out twice a day?
For strength and muscle, the trials found two sessions a day did no worse than one over three to eight weeks.3 They measured performance, not health. If you have a medical condition or a medical question, ask a doctor.
Can I do cardio in the morning and weights at night?
Yes, and the gap is the point: in the rugby trial, a six-hour or full-day gap protected strength gains better than none.6 Lifting first was the order tested there.
Should beginners train twice a day?
None of the trials studied beginners. The ACSM's 2026 primary recommendation is lifting at least twice a week with every major muscle group trained,9 which one session a day covers. How to start lifting weights is the beginner plan.
Are two short sessions as good as one long one?
In these trials, at least as good when the training was split rather than added.2 In practice, two thirty-minute halves of one session is a fair way to use a split day.
If you'd rather not plan it alone
Whether a day holds one session or two depends on the rest of your week. Coaching here is general strength and fitness coaching: the sessions live in an app, built around the gaps you actually have, and a weekly call adjusts the next week from the last one. Coaching for a week that doesn't hold still explains how that works; online coaching covers the rest, and apply is where to start.
General education only, not medical advice. If you have a medical condition, are pregnant, or take medication, check with your doctor before changing how you train or eat.
Sources
- Häkkinen K, Kallinen M. Distribution of strength training volume into one or two daily sessions and neuromuscular adaptations in female athletes. Electromyography and Clinical Neurophysiology, 1994. https://pubmed.ncbi.nlm.nih.gov/8187678/ (accessed October 31, 2026).
- Hartman MJ, Clark B, Bembens DA, Kilgore JL, Bemben MG. Comparisons between twice-daily and once-daily training sessions in male weight lifters. International Journal of Sports Physiology and Performance, 2007. https://pubmed.ncbi.nlm.nih.gov/19124903/ (accessed October 31, 2026).
- Corrêa DA, Brigatto FA, Braz TV, et al. Twice-daily sessions result in a greater muscle strength and a similar muscle hypertrophy compared to once-daily session in resistance-trained men. Journal of Sports Medicine and Physical Fitness, 2022. https://pubmed.ncbi.nlm.nih.gov/33634677/ (accessed October 31, 2026).
- Schoenfeld BJ, Grgic J, Krieger J. How many times per week should a muscle be trained to maximize muscle hypertrophy? A systematic review and meta-analysis of studies examining the effects of resistance training frequency. Journal of Sports Sciences, 2019. https://pubmed.ncbi.nlm.nih.gov/30558493/ (accessed October 11, 2026).
- Pelland JC, Remmert JF, Robinson ZP, et al. The resistance training dose response: meta-regressions exploring the effects of weekly volume and frequency on muscle hypertrophy and strength gains. Sports Medicine, 2026. https://pubmed.ncbi.nlm.nih.gov/41343037/ (accessed October 21, 2026).
- Robineau J, Babault N, Piscione J, Lacome M, Bigard AX. Specific training effects of concurrent aerobic and strength exercises depend on recovery duration. Journal of Strength and Conditioning Research, 2016. https://pubmed.ncbi.nlm.nih.gov/25546450/ (accessed October 31, 2026).
- Schumann M, Feuerbacher JF, Sünkeler M, et al. Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Medicine, 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC8891239/ (accessed October 22, 2026).
- Murlasits Z, Kneffel Z, Thalib L. The physiological effects of concurrent strength and endurance training sequence: a systematic review and meta-analysis. Journal of Sports Sciences, 2018. https://pubmed.ncbi.nlm.nih.gov/28783467/ (accessed October 22, 2026).
- Currier BS, D'Souza AC, Singh MAF, et al. American College of Sports Medicine position stand. Resistance training prescription for muscle function, hypertrophy, and physical performance in healthy adults: an overview of reviews. Medicine & Science in Sports & Exercise, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC12965823/ (accessed October 11, 2026).