Strength training should be a staple of any fitness routine. In addition to increasing muscle strength and mass, regular strength training helps maintain strong bones, improve balance and offers impressive benefits for metabolic health and longevity. These exercises force the muscles to contract against resistance, whether it’s bodyweight, free weights or bands. These repeated movements create microscopic tears in the muscle tissue that our body repairs, which increases the muscle’s strength and size. When designing a strength training routine, the possibilities are endless. Ultimately, the best workout plan for you will depend on your experience, goals and schedule. Full-body routines are designed to work all the major muscle groups in one session. They're beginner-friendly and time-efficient. While this approach can have benefits, there are potential drawbacks, Dr. Ian Smith, physician and author of “Eat Your Age," tells TODAY.com. "You’re not maximizing your efforts for each particular muscle group, because you will get fatigued,“ says Smith. The exhaustion can lead to poor form, which increases the risk of injury, he adds. It's also easier to over-train the major muscle groups, so you may need to take extra rest days. Instead, Smith recommends splitting up your strength training workout into different sessions that train specific muscle groups, also known as "split training" or a "workout split." There are a number of benefits to dividing your muscles and training them on separate days. Benefits of Split Training Split training allows you to devote more time and energy to working on one muscle group at a time for a more intense workout. “You want to make sure that you are isolating as best as possible the particular muscle group that you are working on,” says Smith. One way to do this is to choose multiple exercises that target the same muscles, he adds. These may include bodyweight exercises, lifting weights, or using resistance bands and cables. This can maximize the potential for muscle growth, says Smith, and may help you see more noticeable results. Split training may also reduce the risk of injury because your muscles have more recovery time, Smith adds. If you train each muscle group one-to-two times per week, for example, this allows a minimum of 24-48 hours of rest time. However, there are only so many days in the week. When designing a split training routine, Smith recommends strategically pairing certain muscle groups to train together on the same day. When you train one muscle group, you're working the "primary" muscles, the main ones targeted by the exercise, as well as the "secondary" or accessory muscles, which assist the body during the same exercise. A pull-up, for example, primarily works the latissimus dorsi (lat) muscles in the back, but also engages the biceps secondarily. "It's advantageous to train these on the same day, because you've already put some work in on the secondary group," says Smith. Major Muscle Groups There are about 600 muscles in the human body, according to the Cleveland Clinic, which have different functions. Voluntary or skeletal muscles allow us to control how we move our bodies. These enable us to walk, talk and text. Involuntary muscles move without our conscious control, and facilitate functions like breathing and digestion. Strength training works voluntary muscles, which can be broken into the following groups: Upper body Chest (pectoralis major and minor)Back (latissimus dorsi, trapezius and rhomboids)Shoulders (deltoids) Arms (biceps and triceps) Core Abdominal musclesObliquesLower back Lower body GlutesQuadricepsHamstringsCalves Which Muscles to Train Together There are various types of splits you can do across different days. A popular split is upper body and lower body. However, Smith recommends breaking these muscle groups up further into a push/pull/leg split, which means splitting your strength training into a pull day, a push day and a leg day. Core exercises can get their own day or be worked into any of these days, he adds. "Push muscles": Chest, Shoulders, and Triceps The major pushing muscles are the chest, shoulders and triceps, says Smith. These are the muscles you work during pushups. A push day workout includes many compound exercises, which recruit multiple muscles simultaneously. Exercises that work the "push" muscles — either primarily or secondarily — include: Chest Bench pressPectoral flysCable chest flysDumbbell crossover Shoulders Arnold pressShoulder pressUpright rowForward raises Triceps Tricep dipsForearm plankTricep extensionsTricep kickbacks "Pull muscles": Back and Biceps The major "pull" muscles are the back and the biceps, says Smith. Pull exercises involve pulling weight towards the body, such as a pull-up on a bar. There are a number of exercises which work either the back, biceps or both: Back Shoulder shrugsLat pull-downsBent over rowRomanian deadlift Biceps Bicep dumbbell curlsHammer curlsBarbell row Lower Body: Legs and Glutes Legs should get their own day. "You're just working everything beneath the waist," says Smith. The leg muscles are some of the largest and strongest in the body, which allow us to walk, run, sit and stand. Strong glutes — the main muscles in our butt — are essential for stability and posture. There are a variety of exercises that work the glutes, quads, hamstrings or calves, or a combination of these: Glutes Glute bridgeClamshellsCurtsy lunge Quadriceps SquatsGoblet squatsBulgarian split squats Hamstring Standing hamstring curlReverse lungeSingle-leg deadlift Calves Calf raisesJump squatButt kickers Core "Core you can do any day," says Smith. Core exercises work the abdominal muscles, obliques and lower back. These help improve stability, balance, posture and reduce back pain. If you're prioritizing core strength, you can devote an entire day to core exercises, or incorporate these into your mobility days, says Smith. You can also combine core exercises with another muscle grouping, such as the push muscles. Abs Sit-upsPlanksMountain climbersFlutter kicks Obliques Russian twistSide plankBicycle crunch Lower back V-sit"Good mornings"Bird dog How to Design a Split Training Routine There are many different workout splits. The way you split up your routine will depend on how many days you are strength training, which muscle groups you choose to split, and how often you want to train them. “The average person should do what’s called the 4-2-1 method, and that is four days of strength training, two days of cardio, and one day of mobility or active recovery,” says Smith. Four days of strength training is optimal if you're trying to prioritize muscle strength and growth. "If people are just starting, then try 2-1-1: two days of strength training, one day of cardio, and one day of active recovery. As you build up strength and endurance, the next stage would be 3-1-1," says Smith. Push/Pull/Legs Split Example Day 1: Push: Chest, shoulders, triceps Day 2: Pull: Biceps and back Day 3: Cardio Day 4: Legs Day 5: Cardio Day 6: Push or pull, plus core Day 7: Recovery If you're unsure how to split your strength training routine, talk to a trainer. Consult your doctor or physical therapist if you have a history of sports injuries or underlying health issues.