Still struggling with push-ups? Here are the four most common mistakes that could be holding you back, according to an expert

Push-ups aren't overly complicated, as far as exercises go, but that doesn't mean they're easy. As fatigue mounts, mistakes tend to creep in.

To address these missteps I spoke to Sherri McMillan, the owner of Northwest Personal Training in Vancouver, Washington. Here are four of the most common push-up pitfalls she's encountered over a career spanning more than 35 years, along with her expert tips on how to fix them once and for all.

Four common push-up mistakes

If you need a refresher on form, start with our guide to how to do a push-up .

1. Disengaging your lower back

In a perfect world your shoulders, hips, knees and ankles would remain in a straight line during the push-up, but often the lower back is the first area to cave, allowing the hips to sag and pressure to build at the base of the spine.

Avoid this issue by squeezing your glutes at the start of the move and curling your tailbone under to engage your core and lower-back muscles, and purposefully keep your hips and pelvis rock solid.

“Think about keeping your back flat and elongated throughout,” says McMillan. “Keep your neck neutral throughout too by looking straight down at the floor,” rather than craning to check out your reflection in the mirror.

2. Rushing and no-repping

When staring down 10, 20 or even more than 30 push-ups, it can be tempting to race through them as fast as possible. Why's this a mistake? Because it's unlikely you'll be performing the exercise with a full range of motion—arms completely straight at the top, chest just off the floor at the bottom—meaning your muscles won't be training through their full range, and you'll be missing the gains you might have made with perfect form.

A simple fix is to forget about a rep target and work against the clock instead. “Use a count of 1-2 on the up-phase, and a count of 2-4 on the down-phase,” suggests McMillan.

3. Flaring out your elbows

Hand position and elbow flare are pivotal to a good push-up. If your hands are set too narrow, you'll force your triceps to bear most of the brunt. Too wide and your elbows will flare out, making it harder to retract your shoulder blades.

The sweet spot, says McMillan, is to keep your hands around shoulder-width apart and elbows tucked in close to your body from the first rep to the last.

Why is retracting your shoulder blades helpful? Because by retracting your shoulders and keeping your elbows tucked in close to your body you'll better engage the large mid- and upper-back muscles of the rhomboids and latissimus dorsi.

These antagonistic muscles work in conjunction with your pectorals when performing a push-up, helping you to generate maximum force from your first rep to your last.

4. Overreaching with your hands

To start a push-up you place your hands under your shoulders, right? Well, not so fast. Your hands should in fact be positioned closer to your midline, level with the middle of your chest, to give you the best chance of powering into each rep, says McMillan. Any further and you're putting extra demand on your core to hold everything together.

To get your hand placement spot on, McMillan recommends starting flat on the floor, chest down. Place your hands directly beside your pecs so that your thumbs are brushing your chest. If you can muster the energy, drive up from this position into your first rep, otherwise press your knees into the floor to help you get into your starting stance. Ready? Let's go.