reckonerPlank with alternating leg lifts
A plank with one foot off the floor at a time. Taking a foot away narrows the base you balance on, so your trunk has to stop your hips turning as well as sagging, and the glute on the lifted side works to hold the leg up1. It is the next step for somebody whose plank is already solid, not a first hold.
Hips level and square, lift the leg low.
- Pattern
- Core anti-extension
- Trains
- Abs
- Kit
- Bodyweight, floor
- Loading
- Your own bodyweight
- Reckoner prescribes
- 2 holds of 30 to 60 seconds
- Progression step
- 10 seconds on the hold
- Skill
- Technical
- Recovery cost
- Low
- Not prescribed if you have declared
- Lower back
Muscles worked
How to do it
Start from a plank that is already right
Elbows under your shoulders, forearms on the floor, feet about hip width. Squeeze your glutes and build one straight line from your shoulders to your heels before anything leaves the floor. If your plank still sags before the end of a set, stay with the plank for now.
Lift one leg low
Keep the knee straight and raise one foot a few inches off the floor, slowly. The leg goes only as high as it can without your hips tipping toward the other side or your low back arching. Low and still beats high and wobbling.
Lower it and switch
Put the foot down under control, settle, then lift the other one. The legs take turns inside one hold, so the whole set is one timed effort rather than one side and then the other.
Stop when the hips move
The set ends when your hips start to rock or your low back starts to sag, not when the clock runs out. Log the seconds you held it well.
What goes wrong
Hips turning toward the lifted leg
As the foot comes up, the hip on that side wants to rise and the pelvis rolls open. It feels like a bigger lift because it is one, but the height came from twisting, and holding still against that twist is the point of the exercise.
Kicking the heel high
A high heel looks like effort. Past a few inches most people let the low back arch to get there, and a straight back is the one thing a plank exists to hold. Reach the foot long toward the wall behind you, not up toward the ceiling.
Swapping legs fast
Quick swaps let momentum carry the leg and turn the set into a shuffle, so the trunk never has to hold anything still. Slow lifts, with a beat on both feet between them, keep the work where it belongs.
How Reckoner progresses this lift
Six weeks of this lift, run through the real engine. Nothing below was typed in: the prescription, the decision and the sentence beside it all come from the same code that writes your week.
| Week | Prescribed | What it did |
|---|---|---|
| 1 | 2 x 30 s | Longer hold 30 → 40 sYou held every set with a hard effort and steady form (RPE 7), so the hold gains ten seconds. A hold with nothing in the hands climbs on time, because time is the only axis it has. |
| 2 | 2 x 40 s | Longer hold 40 → 50 sYou held every set with a hard effort and steady form (RPE 7), so the hold gains ten seconds. A hold with nothing in the hands climbs on time, because time is the only axis it has. |
| 3 | 2 x 50 s | Longer hold 50 → 60 sYou held every set with a hard effort and steady form (RPE 7), so the hold gains ten seconds. A hold with nothing in the hands climbs on time, because time is the only axis it has. |
| 4 | 2 x 60 s | Holding steady 60 sYou held every set with a hard effort and steady form (RPE 7), and 60 seconds is the longest this hold goes. There is nothing to put in your hands to make it harder, so this one has run out of room. It stays where it is. If you want to keep pushing here, swap it for a harder movement when the block ends. |
| 5 | 2 x 60 s | Deload 40% of sets offFive weeks of building, then one week lighter. About 40% of the sets come off. The load holds and your reps stay where you earned them, so you keep the strength and lose the fatigue. |
| 6 | 1 x 60 s | Holding steady No changeThe lighter week was for recovery, not a test, so nothing logged in it counts against this lift. It stays where it was before the lighter week. The lighter week is over, so this is back to two sets. |
Real engine output, not an illustration. Every row was produced by running the engine itself when this page was generated.
The full rule, and why the reps move before the load does, is in how Reckoner decides to add weight.
Questions people ask
Is it harder than a plain plank?
Very likely, and the honest answer comes with a gap: no study has compared it with a plain floor plank, so there is no number for how much harder it is. The nearby evidence points one way. In a plank on a ball, extending one hip took the obliques, the deep low back muscles and the glute to very high activation2, and across seven bodyweight trunk exercises a smaller base of support or a one sided version raised trunk muscle activity and how hard people rated the effort3. Taking a foot off the floor does both.
What does it do for the glutes?
More than a core exercise usually does. In a study of 18 exercises, a front plank on the elbows with one leg lifted, knee bent and heel pushed toward the ceiling, produced the highest gluteus maximus activity of any of them1. That version lifts the leg higher than this page asks you to, so read it as the reason the glute works here, not as a number this exercise will match.
When does Reckoner give me this instead of a plank?
Only if you train at intermediate or advanced level. It is never in a beginner's plan. The plank stays the default hold, so this one arrives when you choose it as a swap for the plank, or when the plank and the other easier holds are crossed out or already in your week. It is timed, so you log the seconds you held it. If you tell Reckoner in setup that your low back hurts, it leaves this hold out, and if it ever hurts during training, the pain check brings you back to the plank. A back that hurts is a question for a doctor or physical therapist, not for this page.
Similar movements
There is no load to ease on this lift, so Reckoner offers one of these the first time it stalls. Each of them has a page.
Sources
- Boren and colleagues, International Journal of Sports Physical Therapy, 2011. Electromyographic analysis of gluteus medius and gluteus maximus during rehabilitation exercises 24 healthy adults across 18 exercises, where a front plank on the elbows with one leg lifted, knee bent and heel driven toward the ceiling, gave the highest gluteus maximus activity of all of them, 106 per cent of a maximal voluntary contraction, and 75 per cent at the gluteus medius
- Youdas and colleagues, Physiotherapy Theory and Practice, 2018. Magnitudes of muscle activation of spine stabilizers in healthy adults during prone on elbow planking exercises with and without a fitness ball 26 healthy adults, where a prone plank on a ball with one hip extended took the gluteus maximus, hamstrings, both obliques and the lumbar multifidus above 61 per cent of a maximal contraction, the band the authors call very high
- Andersen and colleagues, Frontiers in Sports and Active Living, 2026. The effect of exercise complexity on trunk muscle activation and perceived exertion during body-weight training in recreationally trained adults 28 trained adults across seven bodyweight trunk exercises, none of them a plank, where a smaller base of support, a longer lever or a one sided version raised trunk muscle activation and the effort people rated