Weight Training: 5 Reasons Why You’re Stronger Some Days Than Others

November 22, 2015 Cathe Friedrich

Weight Training: 5 Reasons Why You’re Stronger Some Days Than Others

Do you find you’re able to lift more on some days than others? Sometimes when you pick up a weight, you feel super strong and ready to tackle your workout – and your performance reflects it. You eke out a few more reps or train heavier than usual. Those days feel great!  Yet on other days, you struggle to lift the amount you usually do. What gives?

A number of factors can affect your weight training performance on a given day. Some days you seem to “have it” while other days you don’t. Here are some factors to be aware of.


Carbohydrates, in the form of glycogen stored in your muscles and liver, are the fuel sources your muscles prefer to use for strenuous activity. Unfortunately, your muscles and liver can only store so much glycogen, so you have to keep replenishing it through diet. If you don’t replace muscle glycogen stores after a workout, and in the time between workouts, you may enter a workout with glycogen-depleted muscles. As you might expect, this can definitely impact your performance. When you have a day where you don’t feel as strong as usual, take a closer look at your diet.

If you follow a low-carbohydrate diet, your performance can suffer since you’re not optimizing your muscle glycogen stores. If you follow a very low-carb diet long term, you may also experience other problems that affect your training like increased cortisol. Unfortunately, cortisol leads to muscle breakdown, a reduction in thyroid function, and decreased production of anabolic hormones like testosterone.

Of course, this doesn’t mean you should load up on high-glycemic carbs to keep your glycogen stores full. Eat more fiber-rich, whole food carb sources like sweet potatoes, moderate amounts of whole grains, fruits, and vegetables to enhance your performance, and be sure to eat a post-workout carbohydrate and protein snack in a 3:1 ratio to rebuild your glycogen stores after an intense workout.

Time of Day

If you train at different times of day, you may notice you’re stronger when you lift at certain times. It’s not your imagination. Your body temperature is higher in the afternoon than it is in the morning. How does this impact your workout? According to research, strength, flexibility and power output are greater in the late afternoon when body temperature is higher. So, you may be able to lift a little more in the afternoon since you’re a little stronger and more flexible. Other research shows muscle strength is lowest in the morning and gradually increases in the late afternoon or early evening.

Despite differences in body temperature, a study published in the Journal of Strength and Conditioning Research showed over a 10-week period, gains in muscle size in response to training were equal between groups who trained in the morning and in the afternoon. So, you may be a little weaker if you train in the morning, but it probably won’t impact how much your muscles grow. Strength may be another story. Time of day and body temperature seems to mainly impact fast-twitch muscle fibers best suited for strength and power.


How well did you sleep last night? The answer can impact your workout performance. A study published in the journal Ergonomics found insufficient sleep decreased performance on four key exercises – leg press, dead lift, bench press, and biceps curls when participants lifted sub-maximally, although maximal biceps curls performance was not affected. Notable was the fact that the participants only slept three hours for three nights in a row, which is a pretty significant reduction in sleep.

Getting less sleep than your body requires, usually between 7 and 8 hours a night, makes it harder to build strength and lean body mass in several ways. You release the greatest quantity of growth hormone during the deepest stages of sleep. If you’re not sleeping enough, you’re probably not hitting those deeper stages for very long. Plus, if you consistently sleep less than you should, your cortisol level rises in response. As you know, cortisol boosts muscle breakdown, making it very hard to gain strength or size. Get your fitness beauty sleep!


One of the cardinal signs of overreaching or overtraining is a decline in exercise performance, including decreased strength. If you’re training a lot and your performance is declining, you may not be giving your body enough recovery time. Keeping a training diary will help you identify when you’re pushing yourself too hard and when your performance is suffering. Overtraining not only endangers your health, by suppressing immune function, it makes it harder to reach your goals. When you overtrain, the stress hormone cortisol rises while anabolic hormones like testosterone drop. That’s not what you want.

Mood and Attitude

Sometimes you simply don’t feel like working out and that can affect your performance. Ask yourself why you’re not in the mood to work out. Is it lack of sleep, stress, or not eating enough? Then address the problem. It’s possible you need a few days off, especially if you’ve been training hard. Skip strength training and do a yoga workout or try something completely new. Boredom is the enemy of getting stronger. Get out your training diary, review it, and set some new goals. Keep your mind stimulated to keep your motivation high.

The Bottom Line

Most people have days where they’re not as strong as they’d like to be. Now you know some of the reasons your performance may not be up to par. Keep in mind that fluctuations like this are natural. You can’t lift your hardest every day – nor should you. Periodizing your workouts is one way to avoid the problem of burnout and boredom. Take advantage of it.



Eur J Appl Physiol. 2010 Apr;108(6):1125-31.

J Strength Cond Res. 2009 Dec;23(9):2451-7. doi: 10.1519/JSC.0b013e3181bb7388.

Journal of Sports Science and Medicine. “Time of Day- Effects on Motor Coordination and Reactive Strength in Elite Athletes and Untrained Adolescents”

Ergonomics. 1994 Jan;37(1):107-15.

Sport and Performance Psychology. “Does Mood Affect Athletic Performance?”


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