Rest Times, the FMS 14 and Kids' Activity: Seven Beliefs Checked

Do short rests burn more fat? Does an FMS score of 14 mean injury? Must kids move an hour every day? Seven fitness beliefs checked against the numbers.

The most quoted number in the Functional Movement Screen was first drawn on a single team of professional football players. Kiesel and colleagues screened them before a season, followed them through it, and found that a total of 14 or less out of 21 went with serious injury more often. That line now gets applied to office workers, runners and teenagers in school sports.

Fitness is full of numbers like that. They start in a study with a specific group and a specific question, and a few retellings later they turn into rules for everyone. This article takes seven of them, three from the weight room, two from movement screening and two from children's activity, and checks each against what the guidelines actually say and what the calculators show when you put real inputs in. Six do not survive in the form people repeat them. One does.

The numbers below come from the Rest Between Sets Calculator, which works from the ACSM ranges, the FMS Score Calculator, which totals the seven tests the way the screen's authors do, and the Kids Physical Activity Calculator, which rates a day against the WHO guidelines by age.

Rest between sets: what the clock should say

"Shorter rests burn more fat"

Checked: mostly not. Standing at the rack for 30 seconds instead of 90 does make the session shorter, and a shorter session is a real benefit. It does not turn a strength workout into a fat-burning one. Lifting while you diet is there to keep muscle, and what keeps muscle is the weight and the reps you manage in the next set. Short rests cut exactly that.

That is why the calculator treats a cut the same way as muscle growth. A compound lift, an intermediate lifter, 10 reps with 2 reps in reserve gets 1 min 30 s whether the goal says muscle growth or fat loss, with a note explaining why. The rest between sets for weight loss page has that example filled in.

So what do short rests buy? Time. A session of 5 exercises at 4 sets each is 20 sets and 19 rests. At 1 min 30 s the calculator puts it at 39 min. Drop every rest by a minute and you save 19 min. If that is the difference between training and not training, take it. Just do not expect the scale to notice.

Rest Between Sets Calculator: muscle growth, compound lift, intermediate, 10 reps at RIR 2, 4 sets of 5 exercises: 1 min 30 s rest and a 39 min session

"There is one right rest time, and it is 60 seconds" (or 3 minutes, depending on who you ask)

Checked: no single number works. The ACSM position stand on resistance training gives ranges, and the range depends on what you are training for. Heavy compound lifts for strength sit at 3-5 min for intermediate and advanced lifters. Muscle growth sits at 1-2 min. Endurance work of 10-14 reps sits under a minute. Inside each range, how close the set came to failure decides where you land.

The table below is the same intermediate lifter on a compound lift, read straight from the calculator for three goals and five levels of effort. RIR means reps in reserve: RIR 0 is a set taken to failure, RIR 4 means four more reps were possible.

Reps in reserve	Strength, 5 reps	Muscle growth, 10 reps	Endurance, 12 reps
RIR 0, to failure	5 min	2 min	1 min
RIR 1	4 min 30 s	1 min 45 s	1 min
RIR 2	4 min	1 min 30 s	45 s
RIR 3	3 min 30 s	1 min 15 s	45 s
RIR 4 or more	3 min	1 min	30 s

Between the longest and the shortest cell there is a factor of 10. Sixty seconds is right for a muscle growth set with four reps left and wrong almost everywhere else. Experience moves the ranges too: a beginner's strength range is 2-3 min, so the same 5 reps at RIR 2 gets 2 min 30 s, not 4 min. Pre-filled versions: rest for strength and 5x5 and rest for muscle growth.

"Curls deserve the same rest as squats"

Checked: no. A set of curls loads one joint and a small amount of muscle. ACSM puts single-joint and assistance exercises at 1-2 min even when the goal is strength. Six heavy curls at RIR 2 get 1 min 30 s; six heavy squats at the same effort get 4 min, well over twice as long. Treating every exercise like the main lift is one of the easiest ways to stretch a 45-minute plan past an hour without doing more work. There is a pre-filled page for rest between isolation sets with an example curl set at RIR 1, which comes out at 1 min 45 s.

The movement screen: what 14 points does and does not mean

"A score of 14 or less means you will get injured"

Checked: it means look closer, not expect an injury. After the first study on football players, a meta-analysis by Bonazza and colleagues pooled the research and found injury odds 2.74 times higher at 14 or below. That sounds decisive until you read the other reviews, which found a weaker link and large differences between studies and populations. An odds ratio describes a group. It does not tell you which person in that group gets hurt, and plenty of people at 13 train for years without trouble.

The calculator reports the total against the cutoff and then moves straight on to what to work on. A screen of all 2s, which is 14 / 21 and sits exactly on the line, gets the verdict "a signal to work on movement, not a diagnosis" and a list that starts with shoulder mobility and the active straight-leg raise, because the FMS authors correct mobility first, then stability, then the full patterns.

"The total is the number that matters"

Checked: the total is the least informative number on the sheet. Two other findings outrank it in the FMS itself: pain, and a difference between left and right. Look at three screens side by side.

Screen	Total	Against 14	What the calculator puts first
Every test scored 2	14 / 21	at the cutoff	shoulder mobility, 2 on both sides
Hurdle step 3 left, 1 right; lunge and rotary stability 3	15 / 21	+1 above	hurdle step, 1 point and an asymmetry 3 / 1
Every test scored 3, shoulder clearing test painful	18 / 21	+4 above	pain: see a clinician before any correction

The best-looking total on that list carries the most urgent finding. Pain in a clearing test scores the whole shoulder mobility test 0, and the screen's authors advise getting a painful movement assessed by a doctor or physical therapist before correcting it with exercises. The 15-point screen passes the cutoff and still has a 3 / 1 hurdle step, which counts as 1 because the weaker side always counts. Read a screen from the notes column, not from the total.

FMS Score Calculator: a 15 / 21 screen above the cutoff with a 3 / 1 asymmetry on the hurdle step, listed first in the order of work

Kids and the activity guidelines

"An hour a day is the rule for every child"

Checked: only from age 5. The hour is the WHO number for children and teens aged 5 to 17, and it is an hour of moderate-to-vigorous activity, the kind that makes them breathe harder. For younger children the guidelines ask for far more time, at any intensity, and they rate the whole 24-hour day: movement, time strapped into a stroller or car seat, screens and sleep.

Age	Activity	Screens	Sleep in 24 h
0-3 months	at least 30 min of tummy time a day	not recommended	14-17 h
4-11 months	at least 30 min of tummy time a day	not recommended	12-16 h
1 year	at least 3 h at any intensity	not recommended	11-14 h
2 years	at least 3 h at any intensity	no more than 1 h	11-14 h
3-4 years	at least 3 h, 1 h of it moderate to vigorous	no more than 1 h	10-13 h
5-17 years	an average of 1 h moderate to vigorous, plus 3 vigorous and 3 strengthening days a week	limit it, no number	not rated here

A 3-year-old who moves for 2 h 30 min, 45 min of it brisk, is 30 min short of the total and 15 min short of the brisk part, even though that day contains far more than "an hour". For babies who cannot crawl yet the only activity guideline is tummy time, 30 min a day spread across the day. The pre-filled pages show these cases: a 2-year-old, a 3-year-old, a teenager and tummy time for a 3-month-old.

Kids Physical Activity Calculator: a day for a child aged 3-4 rated against five WHO guidelines, with the gaps in activity and screen time

"The hour has to happen every single day"

Checked: it is an average over the week. The WHO guidelines for ages 5 to 17 ask for an average of at least 60 minutes a day across the week, which is why the calculator asks for the daily average. A teenager with 84 min of practice on each of five school days and nothing at the weekend has 7 h in the week, the same as 60 minutes every day. Weekly totals are kinder to how families actually live. They are not kinder to the other two parts of the rule, which count days: vigorous activity on at least 3 days and muscle and bone strengthening on at least 3. A teen at 45 minutes a day with 2 vigorous days and 1 strengthening day is short on all three lines at once: 15 min, 1 day and 2 days.

One activity can count twice, which helps. A basketball game is vigorous and strengthens bones in the same hour, so it fills minutes and a bone day together.

The belief that holds up: no screens before age 2

Every list like this needs one belief that survives, and this one does. For a 1-year-old the WHO guidelines do not set a smaller screen limit, they do not recommend sedentary screen time at all. From 2 the limit is no more than 1 hour a day, with "less is better" written next to it, and it stays at an hour through age 4.

The calculator shows what small daily amounts become. Thirty minutes a day for a 1-year-old is 3 h 30 min a week and gets flagged as not recommended. Sixty minutes for a 2-year-old is 7 h a week, exactly the limit. Ninety minutes for a 3-year-old is 10 h 30 min a week, half an hour a day over. The three cases have their own pages: screen time for a 1-year-old, for a 2-year-old and for a 3-year-old.

Age	Screens a day	In a week	WHO
1 year	30 min	3 h 30 min	not recommended
2 years	1 h	7 h	at the limit
3 years	1 h 30 min	10 h 30 min	30 min a day over

The one rule underneath all seven

Each of the six beliefs that failed took a number from a specific setting and dropped the setting. Rest ranges belong to a goal and an effort level, the 14-point line belongs to a group and not to a person, and the hour a day belongs to children aged 5 to 17 and to a week rather than a day. Before using a fitness number, ask who it was measured on and what it was measured for, and put your own inputs in. The calculators below exist for that last step.

Tools discussed in this article

Rest Between Sets Calculator - one rest time from your goal, lift, experience, reps and reps in reserve, plus the length of the whole workout.
FMS Score Calculator - the seven Functional Movement Screen tests and three clearing tests, totalled out of 21 with asymmetries, pain and an order of work.
Kids Physical Activity Calculator - a child's day of activity, screens, sleep and time restrained, rated against the WHO guidelines for ages 0 to 17.