Strength benefits aside, lifting can take a toll on your joints, connective tissue, and nervous system. But studies show that the time of day you train will affect your performance and your physical health. Here are a couple of areas to consider:

1 Your Spine

Intervertebral discs separate the segments of your vertebrae, and they're hydrophilic. That means they have the capability to absorb fluids. Usually, your discs absorb the most fluid while you sleep because your spine isn't being compressed from gravitational force as you stand or sit upright during the day. This is also the reason people are "taller" first thing in the morning.

Taking time to allow the fluid to drain and the discs to properly compress can better prepare the spinal column for action. It's a smart thing to do if strength training is on the menu, especially if you have a susceptibility to back injuries or a history of them.

Think about it. If the discs are filled with fluid, they're less forgiving of twisting, turning, bending, and heavy axial loads. All that fluid adds pressure, and undue pressure can lead to injury.

2 Your Central Nervous System

It only makes sense that there's going to be a training "sweet spot" for your physiology. When we wake up in the morning, we may have energy from a good night's rest, but it doesn't mean that we're at our immediate physiological peak with regards to things like muscle innervations, alertness, reaction time, proprioception, and so on.

Add this to the fact that we've likely been deprived of any nutrients for 10-12 hours and it gives a good reason to avoid lifting heavy first thing in the morning.

If you're someone who habitually trains early in the morning, see if there's a way to make a change – especially if you've been struggling with performance or physique plateaus, injuries, or both, and aren't sure why.

Above all, your recovery and a good night's sleep is paramount for you to continue seeing results, even more so if your schedule just plain doesn't allow you to change your training times to make them more suitable for gains and good health.

For the naysayers who've been strength training at 6AM on empty stomachs and feel great doing it, it's hard to argue against your routine. After all, you don't have any other frame of reference. But you may be holding yourself to a standard of potential that has a lower ceiling based on the handicaps you've unknowingly given yourself. If this applies to you, and if possible, try a week's worth of workouts at a different time and see how it feels.

For those who can't change their schedule, avoid extreme axial loading in the early morning. There's not much good that can come with loading to your 3RM back squat or deadlift 30 minutes after you've woken up.

If you do have to work out in the morning, going hard with movements that involve an appendicular load (involving the shoulder girdle, arms, or legs) and not a direct spinal load will prove friendlier to the vertebrae, and probably the nervous system too.

The morning workout might not be as big an issue for bodybuilders. They can get away with not doing heavy back squats, deadlifts, and barbell overhead presses because there are substitute lifts that can develop the target muscles more efficiently and directly.

Additionally, bodybuilders have much less use for very heavy training in a 1-5 rep range. With that said, the directions apply much more loosely to this crowd.

It would be interesting to see the results for many other anaerobic efforts relative to the time of day they were performed, like the full-out explosive exertion of a 100-meter dash performed at 6AM versus 12PM, versus 11PM.

Canadian strength coach Charles Poliquin once said that most world records are made around 3PM, but I'm not aware of any studies that confirm this. Even so, such a study would have to be performed on elite athletes who have been well trained and earn a living from their sport.

However, most of us aren't elite athletes; we're recreational athletes. Our cortisol levels need to constantly be put in check, we're probably dealing with an old injury or some nagging chronic pain, and any day in the next week could turn into a 15-hour drudgery at work and a sleepless night at home.

Still, if we're going to get the most out of our training, it's time for a reality check. The four or five times per week we spend in the gym has to count, and when we go is half the battle.

Research has supported the idea of two "target times" for great performance:

1. 4 to 5 hours after waking
2. 11-12 hours after waking

For most average people, that means a late morning or lunchtime workout, or alternately, an after-work workout.