When it comes to doing multiple workouts within a 24-hour period, the balance of benefits versus risks can get tricky. Doing too much might lead to increased injury risk, while doing too little may slow your performance progression.
On the one hand, doing a run both in the morning and in the evening or a run in the morning and a strength workout in the evening, can help you maximize your hard days and allow you to get in more weekly mileage—a benefit for many long-distance runners. But push too hard in one of those workouts and it can jeopardize your performance at the next one. Jeopardize too many quality workouts and you risk speed and endurance gains—or worse, injury.
To better help you stack your workouts and figure out where to fit in rest, we asked experts to break down the dos and don’ts. Keep in mind that if you’re just getting started with exercise or working to build your base, it’s probably better to stick with one workout a day, but if stacking workouts fits best into your schedule and you’re ready to elevate your training, here’s what to know to do it right.
Don’t: Make Workouts Intense
In a new study published in Medicine & Science in Sports & Exercise, researchers looked at 17 healthy men and women between the ages of 19 and 31, and asked them to exercise in the morning, the same afternoon, and the following morning. Each of the three sessions consisted of 30 minutes of high-intensity interval training (HIIT) on a bike with work periods done at 80 percent of peak power, or close to 40 minutes of steady-state cycling, done at just over 50 percent of peak power.
After the third session—done in the morning after the previous day’s double—researchers assessed muscle fatigue factors like knee extension, fast-twitch muscle activation, and blood lactate, as well as time trial performance as a marker of endurance.
“Our major findings were that, firstly, endurance performance is compromised if you perform multiple consecutive exercise bouts,” Jenny Zhang, postdoctoral fellow at University of Calgary and study author tells Runner’s World. “This means you might not be able to do as well in a time trial, or you might not be able to complete as many intervals [in a speed workout], so fatigue can ‘accumulate’ as you accumulate exercise sessions.”
The surprising finding, though, was that muscle fatigue recovered between sessions, but central fatigue did not, Zhang says. “Voluntary activation remained depressed at baseline for sessions 2 and 3, which means the central nervous system (brain and spinal cord) had some fatigue, or deficit, in being able to activate the legs after the first session, then wasn’t fully able to recover thereafter,” she explains. “This could potentially also contribute to the compromised performance across accumulated sessions.”
Zhang does note that the study was done on cycling, which doesn’t typically cause as much muscle soreness as running, a more eccentric form exercise (it requires lengthening the muscles under load). So the muscle fatigue may actually be worse for runners, potentially leading to even more performance detriments.
The key note here is that all three workouts were done at a relatively high effort: HIIT sessions or a workout that involves hour-long race pace, Zhang notes.
“Our study supports the idea that fatigue can potentially accumulate across multiple exercise sessions if they are separated by less than 24 hours,” Zhang says. “If you need to do multiple workouts across one to two days and are unable to take much rest time in between, it might be best to separate harder workouts with a lighter one in between, or a different type of workout involving different muscle groups to allow some more recovery.”
Translation: Separate speed intervals or tempo runs with easy runs and lower-intensity strength workouts.
Do: Tailor Your Running Stack to Your Race
Similar to any exercise program, running programs should reflect the needs of the individual and the event they’re training for, according to Rocky Snyder, C.S.C.S., author of strength training guide Return to Center.
“For example, if someone is preparing for endurance events occurring over a 24-hour period, such as a team relay where one person competes for two to three hours and then rests for four to six hours, and then competes again for another two to three hours, and so on, this style of training may have benefits for their future performance,” he tells Runner’s World.
However, that’s a highly specific situation, he adds. If you don’t have back-to-back events on the calendar, you might not need to train this way, particularly if you’re seeing negative effects like more fatigue and increasing injuries.
You also want two-a-days to relate to your current training level and volume, Snyder adds. If you run five days a week, for an average of three to five miles per run, stay within that mileage (or lower) for your two-a-days.
For recreational runners, multiple runs in the same day isn’t usually recommended, says Michelle Quirk, M.D., physician, certified run coach, and host of the Mindful Marathon podcast—that is, unless you’re training based on specific race goals.
For example, stacking runs may come into play if you’re trying to mimic race-day fatigue and run on tired legs, she adds. This can be especially helpful for those marathon training, preparing you for the later miles of the race.
“There is definitely a place for running on consecutive days [especially when race training], but we must balance the training stress with time for recovery, so that the body can adapt to the training and avoid injury,” Quirk tells Runner’s World.
Don’t: Be Afraid to Add Strength to Hard Days
Stacking up multiple runs in a short timeframe may not get you the results you want, but the same can’t be said about doing a hard run and a strength-training session in the same day, says Quirk.
“I like the adage: Keep the easy days easy, and the hard days hard,” she suggests. “That means I would recommend stacking a strength workout on a harder run day. For example, do the track workout or hill repeat workout, followed by the strength training session. Every runner is different, but it’s generally best to run first while the legs are feeling fresh.”
Do: Tune Into Your Body More Closely
When stacking workouts, be realistic about any physical stress that could lead to injuries—for example, tracking delayed-onset muscle soreness (DOMS).
Feeling some muscle aches and stiffness after multiple workouts within a 24-hour period is normal, says Snyder. But if that begins to linger beyond what’s typical for you, pay attention and take a rest day or two for it to resolve. Otherwise, you may be risking muscle strain or overuse injuries.
“The biggest drawback [to two-a-days] would be the increase in both physical and mental load,” Quirk adds. “Without adequate recovery, stacking two hard sessions back to back could lead to fatigue, overtraining, burnout, or injury over time. I always encourage listening to the body and allowing time for recovery.”
In general, Life Time certified run coach, Mike Thomson recommends constant check-ins with yourself to answer whether you’re recovering well. Gauge it by paying attention to your effort level, sleep quality, injuries, even your focus and motivation when running.
Don’t: Avoid Other Aerobic Activities
Although you need to be more in tune with your body and do more tracking of variables like sleep quality and fatigue, workout stacks can offer a performance boost when done well, says Thomson. He tells Runner’s World that while multiple runs in a day might not be advantageous for every runner, that doesn’t mean you can’t stack your days with other, lower-impact aerobic workouts.
“When I think about the year I set many of my PRs in running, it wasn’t from going 70 to 80 miles a week,” he says. “It’s because I added more aerobic time in my weekly training from swimming and biking.” These workouts still allow you to gain the benefits of zone 2 training, while switching up the way your body moves and removing some of the pounding your joints take when running.
Elizabeth Millard is a freelance writer focusing on health, wellness, fitness, and food.