Reassure me that 45 minutes/5 times a week at the gym is enough

If you know your body it's quite easy to judge 25% effort.

I can run 10 intervals at 18k flat and jog at 8 in between. I know it's only 25% as I can recover pretty quickly and my breathing is back to normal by the time my sprint starts again.

Calorie in and expenditure works if you know how quick your metabolism is and how much you burn every second of the day. Doing HIIT means you increase your calorie burn for hours after exercising so it's really hard to work it out.

Of course you'll need to warm up or risk shin splints and other injury. A 4 minute stint on a rower or cross trainer is enough as long as you've stretched. You don't have to go stupidly fast just enough to get the blood pumping.

Sounds like you're doing loads right then.

You may well find that replacing 40min sessions with a reduced number of shorter high intensity runs will actually increase your fitness (waits nervously to get sworn at).

I am worried that you are exercising far too much and not eating at all? Sounds dangerous to me. I hope you are looking after yourself.

On the max effort thing... I was thinking maybe like if a person can run 8 minute/mile pace sustained in intervals, then return to 10 minute/mile pace for the recovery phase (25% slower). Which is something OP could programme into a treadmill, I think, allowing for a 4-6 minute warmup first. Or if maxHR = 160 then return to 120 bpm in recovery phase of run (25% less). Not sure how else those ideas work.

The weight you gain/loose is the balance of calorie intake vs expenditure so its all about reducing your intake to match your new routine. The only problem with "20 minute intense run" is that without proper warmup you risk injury so maybe start with 10 min moderate pace first. Are you able to devote more time in the weekend for stamina/endurance ie longer workouts?

Maybe by tracking heart rate at max speed and heart rate at slowest jog?

How would a runner estimate 'max effort', or 25% of max effort, Twinkie1?

You're supposed to slow down to about 25% of your Max effort level which if you are sprinting as hard as you can should be a slow jog.

Abs Are made in the kitchen not the gym though and you can't out train a bad diet, you just need to be smart utilising your time to increase your fat burn when you're not exercising.

Do you seriously imagine I care what you think about me?

mmm.... I am not exercise expert. But most the running interval advice talks about REALLY slowing down in the recovery phase. Or else no benefits achieved. Walking pace if required. Else a 3 minute recovery phase or getting heart to the very floor of its aerobic range. Whatever that range is (I can't figure mine out so just fudge it).

Sorry if that's no help to OP. Probably are some intense routines online you could experiment with to see what suits you in the 20 minute window.

I'd probably love living in middle east climate if only I could cycle & hike everywhere at dawn. Somehow I sense that's not the done thing.

Running for a long period of time is not as good as HIIT training as you don't continue to burn fat afterwards.

Alongside doing weight training that will increase muscle mass which as well as making you look more defined will mean you burn more calories when doing cardio.

Makes you look like an arsehole though.

All running is 'intense'
Running has a high minimum intensity
Its also easy to measure energy useage compared to strength training

Do 10 runs as fast as you can go with 10 intervals of jogging In between. It's a really good HIIT to keep you fit and will mean you burn fat for hours after you've finished.

Then do a weight set working on a different area each day. Legs, shoulders, chest, biceps and triceps then last day abs.

When someone is just talking out of their arse I feel it is my duty to shoot them down so as to save othe people from believing the bullshit

I could take the time to write an essay explaining things but ffs why should I
the internet it full of info and if anyone is motivated enough to exercise surely they will also want to read up and make sure they are doing things effectively?

Ultimately its no skin off my nose if other people waste their time, being rude is just a quick and dirty way of helping

I also use a heart rate monitor and the point is (hence my suggestion of 30 secs on / 30 secs off) that your heart rate is given time to slow down in your rest period.

If the OP has 20 minutes, I think intervals are the way to go. If you've got time to run a marathon CLEARLY you'll burn more calories / burn more fat.

...I thought for intervals to achieve the ultimate gain (faster averaging running) the important thing was to return to a low recovery running pace inbetween efforts.

I think Kirinm's link says merely "Go by feel" which is way too waffly for me. I use a HRM to make myself get to a recovery run pace.

Clearly if you're running 10 miles you're going to burn more than someone doing 20 mins of HIIT cardio. Christ.

1. Every time I reload this thread that friggin' ad at top bursts into playing & noise. Only this thread, other ads on other threads play soundlessly or don't play at all. I don't know what I did to make this automatic, does anyone know how to turn that off??

2. I read some online claims about kettlebells classes burning more calories than even vigorous running. I was/am fairly but who knows...

I'm doing intervals today, which is why I'm curious what formula Kirinm is using.

Always interesting when someone has to be rude rather than simply disagree. I've not said running doesn't burn calories at all.

OP enjoy what you're doing, 45 minutes is plenty. Just mix it up a bit.