More and more people are shying away from machine-based weight workouts and preferring alternative training methods instead. It seems there has been a general realization that machines are expensive and require a gym membership.

Weight machines also focus on isolation exercises, so they may be ineffective training tools for some people. Relying on machines solely for strength training may actually limit sports performance and increase injury risk during your sports activity.

A great alternative to weight machines are free weights. With these, you don't only get to increase bone density and calories -- you also improve your endurance, power, strength, and increase the size of your muscles.

To get started, here are four simple strength training exercises and how to perform them. 

Concentration Curl

Position yourself on the side of a bench with your legs at an angle of 45 degrees. With your right hand, hold a dumbbell. Begin pushing your right upper arm into your right thigh.  Curl the dumbbell up with your forearm at a 90-degree angle to your leg. Curl the weight up to your chest and then release back down until your arm is almost straight. Repeat the process on the left arm. 

This exercise targets the biceps and brachialis. 

Dumbbell Hammer Curl

This exercise uses a dumbbell on each hand. Start by holding a dumbbell down by your hips. Bend your elbows slightly and hold your arms up and past 90 degrees. Your wrists should be neutral and your thumbs pointing upwards. Release back down to start again. 

This exercise targets the biceps, brachialis, and brachioradialis.

Incline Dumbbell Press

Start by placing your bench at an angle of 45 degrees. To help you stay in position while training, you can raise the seat rest up as well. Hold a dumbbell on each hand then sit right back without back arched. Your feet should be pressed into the floor. 

Now bring your hands into a bench press position. Your elbows should be at a 45-degree angle to your body and the weights around chest height. Start pushing the dumbbells up and towards each other so that they meet slightly above eye level. Bring them back down and repeat. 

This exercise targets the triceps, delts, and pecs.

Dumbbell Shoulder Press

Set your bench in an upright position then sit back holding a dumbbell on each hand. Then ready your arms up to push the weights above your head. Bring your arms up ready to push the weights above your head. The dumbbells should be at around ear height with your arms at a 90-degree angle to your body. Now push them up together so they meet above your head then bring the weights back down. Your back should be straight and your hips pushed back into the bench. 

This exercise targets the traps, delts, and triceps. 

Beginners should always use light dumbbells first. Once you get the hang of your routine, you can add weight from there.