You could also, if you have a gymnastic, athletic or strength skill, try and use that provided you get more toned.
If you want to see how far you could go - if you really push the skill, look at AnnaRose on my port - she has lots of options open to her
She is though at a very high standard.
It has to be believable - I have seen models who invest all their time in building muscle but cannot pose for toffee. What photographers are particularly interested in is people who can put it all together
She did ask for advice on how to become one, which I would presume would involve gym time to gain the ideal body for that type of modelling.
Just because you might think she is not suitable right at this minute doesn't mean she wont be perfectly suitable in 6 months time.
Although your comment may actually help her, when people are that cockish to me I put in even more effort to prove them wrong.
How do you know how fit she is?!! For all you know she could run 10 miles a day!
I'm not toned but I'm fit...I run, I go boxing and I ride horses plus do all the hard work that goes with them. When I decided to start doing serious working out several years ago, within a matter of weeks I could see the difference and it was because I was already quite fit so it didn't take me so long. If she wanted to be a fitness model, with the right regime I don't see why she coudln't make it! Hell, with time and practice, you could make a good photographer!
Keltica may have been harsh, but the point still stands.
OP, you really need to hit the gym and HARD. Being slim does not equal being fit, nor does it automatically make you toned. Get a personal trainer who can set you achievable goals with your body - you will probably need a TOTAL lifestyle overhaul...a friend of mine takes his own pre-prepared fresh meals to social events, goes to the gym when most normal people are asleep or partying and is generally insanely committed to getting results.
My advice would be to find some photos of the sort of fitness models you are aiming at. Take the photos to a decent personal fitness trainer and ask them what you would need to do to achieve the same body shape (and how long it would take). Then decide if the benefits outweigh the cost/effort.
I am not sure what the OP is thinking of some or all of the advice so far and didnt specify what sort of fitness modelling she was interested in - she just wanted to know what she should consider.
Well appearing fit and toned is one requirement. Fitness modelling can be anything from looking pretty in a tracksuit at an event to modelling extreme sports and gymnastics.
Some of the advice is uneducated - I wouldnt mind betting from your shape you are mesomorphic which if you are, means you already have muscle and it would not be massively difficult to bring it out. But none of us can tell from your port but you did not ask for that assessment anyway.
You do need to decide what you would like to do, and get some advice [not from this site] on what sort of training routine would help - you may find that aerobic training is just as important as using weights.
You also need to develop the posing skills to show confidence and fitness.
The worst thing you can do is just hit the gym. It may not be necessary and there are models who do that and they may have muscle, but they do not look like fitness models.
The model I showed you on the first page does not spend hours and hours in the gym. She doesnt need to. SHe has the right body type, and puts regular effort in and is a skilled gymnast. SHe can lift her whole body off the floor and hold a pose which virtually no other model on PS can do, yet she does not spend her whole life training.
My actual advice would be go and find someone who knows what they are talking about.