You eat right (usually), get enough sleep (mostly), and make sure to listen to your favorite tunes (hey, your Justin Bieber pick is between you and your iPod).
And yet some days your workouts just aren't, well, working. What gives? Truth is, there are all kinds of little factors that can make or break any given sweat session.
Here are 10 surprising things that can change the way your body responds to your exercise routine—and how to fight back.
1. Location, location
Few people would disagree that running in a cramped, sweaty gym doesn't exactly compare to exercising outside in the fresh air. Turns out, that good feeling isn't just in your head. A 2011 study published in Environmental Science & Technology shows that outdoor activity comes with greater decreases in tension, anger, and depression. Plus, outdoor exercisers are also more likely to stick with an exercise habit.
The outdoor perks extend to your body, too. "In addition to the psychological benefits, the hard ground makes leg muscles stronger than running on a treadmill," says Kay Porter, sports psychologist and author of The Mental Athlete.
2. All by yourself
If you usually work out alone, joining a group of like-minded exercisers may boost your results, finds an Oxford University study. Rowers who worked out in teams experienced a greater endorphin release and had a higher pain tolerance than rowers who worked out alone. "It's easier to get up and out if you have a group or buddy to join up with," says Porter. "You feel more connected, which adds a social component of fun and interaction."
3. That time of the month
Hormonal shifts during a woman's menstrual cycle creates more laxity or "give" to muscles at certain times, putting her at a greater risk of injuries (particularly to the knees), says Dr. C. David Geier, Jr., director of sports medicine at the Medical University of South Carolina. "This is often seen during ovulation, when estrogen levels are higher."
And while it's still unclear exactly what the relationship between female hormones and injuries is, women tend to have a much higher incidence of ACL (anterior cruciate ligament) tears in general, says Geier. This isn't a pass to skip exercise when you're ovulating, of course, but it's a good call to consider more gentle workouts during that time, such as these three joint-friendly routines (that still torch some serious calories).
4. The time of day
If you can't get out of bed for an early morning workout, don't fret. Afternoon sessions may be more beneficial (and even offer anti-aging benefits!), according to a new animal published in the Journal of Physiology. How? Exercise may reset processes that generate our brain's daily rhythms of sleep/wake cycles, which change as we age, says lead study author Christopher S. Colwell, a professor at UCLA Medical School. The study found that exercising in the afternoon produced greater benefit than working out first thing in the morning.
5. Weather woes
If you find it easier to breathe during warm weather exercise, you're not alone. Exercise-induced asthma causes wheezing, coughing and chest tightness, and it occurs more frequently in cold, dry air (think skiing, skating, and running in the winter), says Dr. Kevin McGrath, a fellow of the American College of Allergy, Asthma and Immunology. "It's due to hyper-cooling and drying of the airways with exercise, and usually starts eight to 12 minutes into exercise."
Warming up first makes exercise-induced asthma less likely, as does using an inhaler 15 to 20 minutes prior to exercise, says McGrath. (Get your body going with this Perfect Warm-Up.)
6. OTC medications
Drinking and working out clearly don't mix, but some seemingly harmless over-the-counter medications can also change your body's response to exercise, as well as upping your risk of injury. OTC drugs to use with caution include cold and flu medicines containing pseudoephedrine, which can cause drowsiness, as well as some allergy meds. "Plus, ibuprofen and decongestants can raise blood pressure in some people," says Jill Sailors, PharmD, assistant professor of pharmacy practice at St. Louis College of Pharmacy, Missouri. Talk to your doc about the best time to take your meds and work out.
7. You're too fit
The good news: you're in great shape. The bad news: you'll have a harder time seeing additional results from your workouts. "Either a plateau is at work or the Principle of Diminishing Returns," says Fabio Comana, director of continuing education for the National Academy of Sports Medicine. According to this theory, as you become fitter, you'll see reduced improvements as you approach your genetic limits—you'll need to work harder to see the same gains. Comana recommends taking a short break from training or changing your routine to take your fitness to the next level.
8. You're foggy about recovery
When it comes to exercise, you can have too much of a good thing. Your body needs regular breaks to recover, repair, and restore. "This takes rest, nutrition, sleep, and managing stress," says Comana. While recovery time varies, generally muscle endurance training (e.g., yoga) requires 24 to 36 hours between sessions, and strength training takes 48 to 72 hours. Cardio (moderate) usually requires 24 to 36 hours, although more intense, high-intensity training may require 48 hours or more for recovery, says Comana.
9. A bad high school gym teacher
Negative attitudes toward exercise may stem from a humiliating phys ed experience from years ago, finds a 2010 study from the University of Alberta. Researchers determined that a lifelong negative attitude can stem from being under the thumb of an unfair, negative, or humiliating coach or gym instructor as a child. While you can change the past, of course, you can choose to surround yourself with positive gym-goers and encouraging classes today.
10. Hot hands
Another reason sweaty palms are annoying? Hot hands can cut your workout short, finds a small study presented at the American Heart Association Metabolism 2012 session. Women who exercised with their hands in cold, 60-degree water worked out longer than women whose hands were in 98-degree water. In fact, the "cooler" women dropped nearly three inches from their waists, were able to walk faster, and had lower resting blood pressure than the control group over a 12-week period. Freeze a water bottle overnight to carry with you on your next walk.
Linda Melone is a certified strength and conditioning specialist.