What 30 days can and can't changeEmerging evidence
The likely gains are a longer hold and steadier control. In one small study of 30 novice weightlifters with no control group, 8 core training sessions over 4 weeks took their plank from about 56 to about 115 seconds. In a randomised trial of 21 male college athletes, 8 weeks of extra core training raised a plank-based endurance test from about 194 to 242 seconds, and in a randomised trial of 61 young adults, 12 weeks of 1-minute holds of three kinds of plank, 3 days a week, improved sit-up endurance by about 55% against people who didn't train.
These studies were small, and much of an early gain in a hold is getting used to the test and the discomfort. A flatter stomach isn't on the list.
Sources 11, 12, 13, 14
Why side planks and bird dogs tooEmerging evidence
The front plank trains your trunk against sagging. Side planks train it against bending sideways and bird dogs train your back, and each has its own normal hold times: in 75 young adults, side-plank times were well below back-muscle endurance times. In 117 adults with and without back pain, those with back pain whose back-of-body endurance was greater relative to their plank time had less disability, and in a lab study of 12 abdominal exercises, none trained every abdominal muscle while keeping spine load low.
Sources 15, 16, 17
Planks and back painStrong evidence
Across 29 trials, core exercise helped long-term low back pain about as much as other exercise, not more, and across 249 trials, exercise in general cut pain by about 15 points out of 100 against no treatment, usual care or placebo. A longer plank isn't a sign of a healthier back: in 117 adults, people with back pain actually held longer planks than people without.
Sources 18, 19, 16
Planks don't flatten your stomachMixed evidence
In 24 adults, 6 weeks of abdominal exercise didn't reduce belly fat, and in 40 women, adding abdominal training to a diet took off no more than the diet alone. Two small trials found some local fat loss, but only with far more abdominal work than any plank challenge: 57-minute sessions of running with weighted crunches and torso rotations, 4 days a week for 10 weeks, in 16 men, and an 8-week circuit in 14 people.
Fat comes off with overall activity and eating less, not from the muscle you train.
Sources 20, 21, 22, 23
Older adultsEmerging evidence
No study gives plank norms for each age, such as for a 65-year-old. In 120 adults, people aged 60 to 79 held a plank for less time than people aged 20 to 35, and the test gave much the same result on two occasions. Start on the knee track, aim for repeated holds of 20 to 30 seconds with good form, and compare yourself with yourself.
Source 24
After birth, in pregnancy and with heart failureStrong evidence
After giving birth, the NHS advises avoiding sit-ups, planks and high-impact exercise to start with and beginning with gentle tummy exercises. See a GP if the gap between your tummy muscles is still obvious 8 weeks after the birth, and see our postpartum and diastasis recti guides for when planks come back. In later pregnancy, avoid lying flat on your back for more than a few minutes, and use kneeling and side-lying core work.
With heart failure, the British Heart Foundation advises avoiding holding your breath and exercise that uses your whole body as a weight, such as press-ups or planks.
Sources 25, 26, 27
Check first if this applies to youStrong evidence
Before the day 1 test, answer the PAR-Q+ (the Physical Activity Readiness Questionnaire for Everyone): a yes to any of its questions leads to follow-up questions that may send you to your doctor or a qualified exercise professional first. The World Health Organization notes that people without such problems generally don't need a medical check before light or moderate activity.
With ME/CFS (myalgic encephalomyelitis or chronic fatigue syndrome), NICE (the National Institute for Health and Care Excellence) advises against general exercise programmes and fixed increases, which is what a challenge is. With osteoporosis, the UK consensus advises avoiding a lot of forward bending of the spine: planks keep the spine straight, which is our reading, but keep the McGill curl-up small or skip it, and with spinal fractures ask a physiotherapist first.
Sources 28, 29, 30, 31
Warning signsStrong evidence
Call 999 (911 in the US) for chest pain that doesn't go away, spreads to your arms, neck, jaw, stomach or back, or comes with sweating, feeling sick, light-headedness or breathlessness. Ask for an urgent GP appointment or contact NHS 111 (in the US, urgent care) for back pain with feeling hot, cold, shivery or generally unwell, or severe back pain that starts suddenly or gets worse quickly.
Sources 32, 7
After the 30 daysEmerging evidence
A challenge is a start. In an evaluation of a 24-day push-up challenge in Australia, physical activity was a little higher 2 weeks after it ended but no higher 3 months later, and habits take longer than 30 days to form: in the four studies of a review that timed it, the typical time was 59 to 66 days, ranging from 4 to 335.
Choose your next step before day 30: keep 2 or 3 core sessions a week with our beginner core workout, the ab workout with no equipment, the advanced core workout or the McGill big 3, or try the 4-week beginner Pilates plan.
Sources 33, 34