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If you want to jumpstart your fitness routine, Katie Austin is here to help. She is a trainer, health coach, author, and Sports Illustrated Swimsuit model. She even has her own app with options for every fitness level and mood. Choose from a wide variety of workouts including HITT, pilates, yoga, and dance.

She explained, "The Katie Austin App is a must-download for people at all fitness levels because it provides customized workouts, variety, convenience, community, recipes, live workouts, and expert guidance. It can help you stay motivated, stay accountable, and achieve your fitness goals, no matter where you are on your fitness journey. All you have to do is press play and follow along!"

In an exclusive E! interview, Katie discussed her app, fitness insights, and the workout must-haves she keeps in her gym bag.

Katie Austin's Fitness Must-Haves

"I always like to have a hairbrush on hand– especially if I need to shower and run out super quickly."

Katie's pick has 47,700+ 5-star Amazon reviews and it comes in 27 colors and patterns.

"It never hurts to have something comfy on hand to change into or throw on if you're in a rush!"

This set also comes in black.

"I like to be as sustainable as I can, so I keep a reusable bag on hand to put my sweaty clothes in after I change at the gym!! It can literally be a reusable tote, drawstring bag, or whatever you have laying around! I especially love when they're machine-washable so you can toss them in right with the dirty laundry."

Katie's pick comes in 15 colors and patterns.

"Staying hydrated is important! So, I always carry a refillable water bottle like this one from Stanley to ensure I'm being sustainable and hydrating properly!"

"I love having a hairband in my bag to keep my hair slicked back and out of the way, so I don't have to worry about it during my workouts!!"

This headband comes in three colors.

"I always need super comfy socks so that I'm set up for success with every workout!"

"I love having a super clean body cream on hand that helps make sure my skin is feeling refreshed after a workout, especially after sweating it up!"

Katie Austin's Gym Bag

This bag comes in a ton of colors and it has enough room for all of your fitness essentials.

Katie Austin's Fitness Q&A

E!:Why is The Katie Austin App a must-download for people at all fitness levels?
KA: The app provides customized workout plans that are tailored to your fitness level, goals, and preferences. This ensures that you get the most out of your workouts and can progress at a pace that is right for you. The app offers a wide variety of over 230+ on-demand workouts. This means you can mix up your routine and try new things to keep your workouts fresh and challenging.

With the app, you can work out anytime, anywhere. You can tune in with me each week to workout live or you can even download workouts ahead of time to work out offline.

E!: Did you change anything about your routine to prep for the Sports Illustrated Swimsuit shoot?
One thing I love most about SI Swimsuit is their encouragement to be your most authentic self and showcase it. So, when it came time to prep for my SI shoot, I didn't do an entire overhaul of my lifestyle, but rather focused on things that were already important to me! I ate a balanced diet, worked out, and prioritized my mental health and routine!

When it came to my diet, I didn't want to restrict myself from indulging in foods and my normal diet because I wanted to focus on the habits rather than cutting off "bad foods" cold turkey. I ended up giving myself a "kitchen curfew" of 8:00 PM, so that my body could digest dinner before bed, making it easier to get a better night's rest and to wake up more energized!

E! What advice do you have for someone who wants to get into fitness, but is nervous to get started?
KA: I can understand how starting your fitness journey can seem super intimidating, especially if you're newer to exercise or just haven't been active in a while. Here are a few tips to help:

• Start small and work your way up gradually. Every athlete starts somewhere. You don't have to jump right into an intense workout routine on your first day. 
• Find an activity you enjoy. If you hate running, you're not going to stick with a running program for very long. Instead, try different types of exercise until you find something you enjoy. 
• Set realistic goals. Don't expect to lose 20 pounds in a week or run a marathon in a month. Set small, achievable goals that you can work towards over time. For example, aim to walk for 30 minutes a day, or to do 10 push-ups without stopping. Celebrate your successes along the way, no matter how small they may seem.
• Get support from others. It can be helpful to have a workout buddy or join a fitness class or group. Having others to exercise with can provide motivation, accountability, and a sense of community. You can also seek support from online forums, social media groups, or fitness apps - like the Katie Austin App.
• Remember that progress takes time. Fitness is a journey, not a destination. It takes time and consistent effort to see results. Don't get discouraged if you don't see changes right away.
• Be kind to yourself. Remember that nobody is perfect, and everyone has setbacks and struggles. Don't beat yourself up if you miss a workout or indulge in a treat. 
• Stick to a schedule or program: Take the mental strain out of it! Sticking to a routine and carving out designated times to do your workouts makes it so much easier to keep up! With the Katie Austin App, you have the ability to follow along with our weekly workout schedule or the flexibility to schedule your own workouts.

E!: What is your favorite piece of advice you like to share when it comes to feeling your best self?   
KA: You don't owe anyone an explanation for doing what's right for you. Take note of who you're around and where you are when you feel your best self. Lastly, of course, move your body for your mental health!

If you're looking for more fitness must-haves, you'll love these activewear pieces from Reese Witherspoon's brand Draper James.

(This interview has been edited and condensed for length and clarity.)