I gained a pound this week, starvation mode?

I'm 5ft 8", narrow build, start weight 136lbs, now 133lbs, goal 126lbs. I track food every day and weigh the food where necessary. Workouts are one HIIT session w personal trainer where I am dripping with sweat, 1 body pump, 1 step, 1spin then 2 runs and another gym session. I exercise 6-7 days a week. Prior to dieting 3 weeks ago I exercised 4 times a week and some sessions not that intense so I have really upped the ante now. I want to tone up, I have major muffin top at moment.

With all that exercise I would be eating around 2000 and still be losing. You need to eat more and also ignore the scalers and go bu your measurements. You have a PT so ask them to measure your body fat.

A fluctuation of just 1lb is not enough to go on, it's probably water weight.

However, eating just 1000 cals when you only have 10lbs to lose is not a good idea. Aiming to lose quickly usually results in the weight returning just as fast when you increase your cals or slip back ino eating what you were previously. You also risk losing lean muscle mass rather than just fat, so you might weigh less but your BF% will remain about the same or even increase proportionally to your weight.

In the very least you should be eating back your exercise cals on top of the 1000 cals you're currently eating.

I'm 5ft 8", narrow build, start weight 136lbs, now 133lbs, goal 126lbs. I track food every day and weigh the food where necessary. Workouts are one HIIT session w personal trainer where I am dripping with sweat, 1 body pump, 1 step, 1spin then 2 runs and another gym session. I exercise 6-7 days a week. Prior to dieting 3 weeks ago I exercised 4 times a week and some sessions not that intense so I have really upped the ante now. I want to tone up, I have major muffin top at moment.

STOP DIETING. RIGHT NOW!

Eat at maintenance or SLIGHTLY below, get on a heavy lifting program, get adequate protein. You will recomp your body. Upping your intense workouts and eating extremely low calories is only going to cause you to lose LBM.

I can guarantee if you lift heavy for 8 weeks, with a little moderate cardio tossed in only if you want to, eat almost maintenance and at least 100g protein per day, that you will like your body at 133lbs WAAAAAAAAAAAAAAAAAAAY more than what you're going to see at 126lbs doing crazy intense Cardio workouts... because literally everything you are doing right now is cardio... yes even the Body Pump. Protein and lifting maintain muscle or at the very least minimize loss of muscle while eating below maintenance calories to a certain extent. You're constantly eating below BMR and aren't going to get the "toned" results you are looking for by going down that path. You're going to be low weight with a high BF% still.

Your body is having a wonderful time dining on your muscle mass while you are eating at a nearly 1000calorie deficit.

I'm 5'8, 165lbs, 25% bodyfat, down from 198lbs, 30+% bodyfat and I've done it by eating at least 1600, usually closer to 1900 cals a day and most of my workouts being heavy lifting. Also, check into your goal weight, 126 is on the low end for women of our height.

You're not in starvation mode. You just need to poop.

Unless you are a small child or a midget, eat at least 1200. Ok?

you gonna offer the girl some advice or just go with this snarky retort stuff?

I wasn't trying to be snarky, I was trying to be helpful. But here is more info.

You did not gain 1 actual pound unless you ate 3,500 calories over your TDEE which you clearly could not have done if you have only been eating 1000 calories a day. Weight fluctuates, especially for women. Don't use only the scale to measure progress, take pictures and use your measuring tape.

Educate yourself on BMR and TDEE and learn that eating less than 1200 calories is not healthy.

You're not in starvation mode BUT you're not eating enough. Eat 1200 mnimum plus your exercise calories, or set MFP to very active and losing 0.5 lb a week and go by that.

As for the added weight its what others have said - water and poop. Or just being female.

I'm 5ft 8", narrow build, start weight 136lbs, now 133lbs, goal 126lbs. I track food every day and weigh the food where necessary. Workouts are one HIIT session w personal trainer where I am dripping with sweat, 1 body pump, 1 step, 1spin then 2 runs and another gym session. I exercise 6-7 days a week. Prior to dieting 3 weeks ago I exercised 4 times a week and some sessions not that intense so I have really upped the ante now. I want to tone up, I have major muffin top at moment.

STOP DIETING. RIGHT NOW!

Eat at maintenance or SLIGHTLY below, get on a heavy lifting program, get adequate protein. You will recomp your body. Upping your intense workouts and eating extremely low calories is only going to cause you to lose LBM.

I can guarantee if you lift heavy for 8 weeks, with a little moderate cardio tossed in only if you want to, eat almost maintenance and at least 100g protein per day, that you will like your body at 133lbs WAAAAAAAAAAAAAAAAAAAY more than what you're going to see at 126lbs doing crazy intense Cardio workouts... because literally everything you are doing right now is cardio... yes even the Body Pump. Protein and lifting maintain muscle or at the very least minimize loss of muscle while eating below maintenance calories to a certain extent. You're constantly eating below BMR and aren't going to get the "toned" results you are looking for by going down that path. You're going to be low weight with a high BF% still.

Your body is having a wonderful time dining on your muscle mass while you are eating at a nearly 1000calorie deficit.

I'm 5'8, 165lbs, 25% bodyfat, down from 198lbs, 30+% bodyfat and I've done it by eating at least 1600 cals a day and most of my workouts being heavy lifting. Also, check into your goal weight, 126 is on the low end for women of our height.

Sounds like you found a smart woman to give you advice -- I'd listen.

Actually you need to eat to lose weight. Your body is conserving. You said you are working out hard, maybe you are not getting enough calories to support you metabolism. Try to relax and focus on how your clothes fit, how you feel not just the scale that is only one piece to the puzzle. If you are working out hard you may need closer to 1400-1600 calories/day. The mind is a very powerful thing and my trainer told me about a study or an article where people worked out and did not lose weight but then went on vacation and did because they were so intense about the weight loss when not o vacation they concluded it was that aspect that kept the weight on. Keep going strong it will come.

Don't see any water intake, are you drinking plenty of water?

Everyone says "starvation mode myth" but it makes me wonder why people with 700-900 Net calories per day are always asking why they aren't losing weight like the OP but women and men eating 1500+ lose consistently...