Not a running coach but I am a bit of a cycling coach and intervals are a thing there too, at similar scales (anywhere from 45s to 3m of hard-as-you-can effort, and then just enough recovery that the next effort can also be as hard as you can), starting with shorter intervals and moving towards longer ones.
A few things jump out at me. First the good: you should in fact be barely able to get to the end of the interval. In fact I usually try to trick myself by saying I'll do a somewhat shorter one, like 2.5 minutes instead of 3, and then at the end when I feel like I can't continue, see how much longer I can go at that effort. Sometimes I make it the rest of the way and sometimes I don't. On a good day I get to 3 minutes feeling like if I tried to keep going to 3:05 I'd puke.
But the bad is: if it feels like you're not able to get to the end out of weakness and not because of pushing yourself, you might need to adjust some of the parameters of the workout. Maybe 90s is too long for the short interval (I know it is for me, and I do 45s for my short intervals). Maybe you're not letting yourself recover enough during the walk, and you need to walk slower or use a longer recovery time. Maybe it's better to do two or three short intervals followed by two or three long ones. Maybe the long intervals shouldn't be the same effort all the way through, but consist of alternating 30s to 45s efforts at 100% and 80% or 90%. Maybe a passive treadmill is just enough worse on your body that an electric one is better, or maybe treadmills are just not where you can push yourself. There's no one size fits all answer.
Do you have a heart rate monitor? I'd love to see a graph of your heart rate, or failing that then at least numbers for the midpoints and endpoints of the runs, and the endpoints of the walks.
no subject
A few things jump out at me. First the good: you should in fact be barely able to get to the end of the interval. In fact I usually try to trick myself by saying I'll do a somewhat shorter one, like 2.5 minutes instead of 3, and then at the end when I feel like I can't continue, see how much longer I can go at that effort. Sometimes I make it the rest of the way and sometimes I don't. On a good day I get to 3 minutes feeling like if I tried to keep going to 3:05 I'd puke.
But the bad is: if it feels like you're not able to get to the end out of weakness and not because of pushing yourself, you might need to adjust some of the parameters of the workout. Maybe 90s is too long for the short interval (I know it is for me, and I do 45s for my short intervals). Maybe you're not letting yourself recover enough during the walk, and you need to walk slower or use a longer recovery time. Maybe it's better to do two or three short intervals followed by two or three long ones. Maybe the long intervals shouldn't be the same effort all the way through, but consist of alternating 30s to 45s efforts at 100% and 80% or 90%. Maybe a passive treadmill is just enough worse on your body that an electric one is better, or maybe treadmills are just not where you can push yourself. There's no one size fits all answer.
Do you have a heart rate monitor? I'd love to see a graph of your heart rate, or failing that then at least numbers for the midpoints and endpoints of the runs, and the endpoints of the walks.