Is there anything exercise can't do? It helps people lose weight and sleep better, as well as aids in the prevention of colds and disease. And aside from the endorphins it creates to uplift moods and energy levels, hitting the gym can also reduce stress. With all these benefits, it would seem that more is better — but is that really the case?
To stay healthy, experts recommend about 30 minutes per day  of moderately intense exercise five days a week. If you're trying to lose or maintain your weight, 60 to 90 minutes a day, five times a week is the goal, and we're talking heart-pumping, calorie-burning cardio.
With that said, it's not always possible to fit in five workouts each week, so doubling up in one day is a great way to balance a tight schedule. When doing two daily workouts, make sure they're different from one another so you can include a balance of cardio, strength training, and stretching over the course of a day. Go for a run in the morning and take an evening yoga class, or hit up that lunchtime Spin class and do some strength training before dinner. Be conscious of which muscles you're targeting each time you exercise, because solely working your legs twice in one day could not only cause a muscular imbalance that leads to pain or injury, but you'll also get bored. Rest days are also important, so take it easy at least twice a week to allow your muscles a chance to heal and strengthen.
Of course if you're training for a race, tackling a daylong hike or snowshoe, or attending a fitness event, you'll be exceeding the two to three hours of exercise two basic workouts would entail. For big fitness bursts like this, pace yourself throughout the day and be mindful of pushing yourself too far. If you're feeling extremely lethargic, dizzy, nauseous, or painfully sore, stop immediately to rest, and the next time scale down the intensity a bit. If two regular daily workouts is something you'd like to make a habit of, it's a good idea to stick to 30 to 90 minutes per session, and make one high-intensity cardio and the other lower intensity.
Also keep in mind that exercising twice in one day will cause you to burn more calories, and make sure you're nourishing yourself with enough protein and healthy carbs. And as long as getting in your two workouts doesn't have a negative effect on your life  or prevent you from getting enough sleep, then there's nothing wrong with sweating it out twice (as long as you're OK with taking two showers!).