Although selectorized machines are often easier than free weights for beginning exercisers, some weightstack exercises require extra attention on the trainer's part to make sure the user is safe and remains injury-free. This breakdown of exercises will help you to train your clients effectively.
WEIGHTSTACK MACHINES typically provide body support and fixed movement patterns, which may make exercise performance safer and simpler than free weights. Nonetheless, certain machine exercises may be contraindicated for some individuals, and other machine exercises may need to be modified for optimum performance and results. If you train clients on weightstack machines, consider the following selected exercise analyses and recommendations.
Chest cross machine
Chest cross machines that have vertical movement pads for elbows and hands place the shoulders into externally rotated positions, which may cause injury to the rotator cuff muscles (teres minor and infraspinatus). To reduce the risk of shoulder problems, choose chest cross machines that keep the forearms parallel to the floor or angled downward. These arm positions require neutral or internally rotated shoulder joints, and are equally effective for muscle development with less joint structure stress.
Prone leg curl
Due to the extended hip position, prone leg curl machines may place excessive stress in the low-back area of some clients. If available, switch to seated curls so the hips remain flexed throughout the exercise. Although seated leg curls offer slightly less movement range, they provide essentially the same conditioning benefits for the hamstring muscles. To further reduce low-back stress, make sure clients keep the entire back in contact with the supporting seatback throughout the exercise.
The overhead movement pattern employed in shoulder press machines may be accompanied by back arching, which may, in turn, lead to low-back problems. To reduce stress on the low-back area, clients should make every effort to keep the entire back in contact with the supporting seatback throughout the exercise. If this is too difficult, they should switch to the incline press exercise. Although the incline press places more emphasis on the anterior deltoids than on the middle deltoids, it is, nonetheless, a highly productive shoulder exercise that reduces stress to the low-back area.
The pullover exercise may cause uncomfortable arching on the lower back during the upward movement phase, as the elbows move above head level. One way to avoid the arching action is to reduce the upward movement range by stopping each repetition when the elbows are alongside the head. Another option is to substitute with the seated row exercise, which is executed with the elbows below shoulder level. Although this linear movement includes the biceps muscles, it can be a very effective exercise for the latissimus, dorsi and teres major muscles.
The seated row exercise has different applications, depending largely on which movement handles are used and which movement planes are engaged. For example, if your client grasps the vertical handles and pulls the upper arms back in the vertical plane (shoulder extension with arms near sides), the prime mover muscles are the latissimus dorsi and teres major, along with the biceps. However, if your client grasps the horizontal handles and pulls the upper arms back in the horizontal plane (horizontal shoulder extension with arms away from sides), the prime mover muscles are the posterior deltoid and biceps muscles, along with the latissimus dorsi and teres major. The horizontal pulling position also lends itself to a more fully retracted shoulder girdle that enables greater emphasis on the middle trapezius and rhomboid muscles. When clients are using seated rowing machines that incorporate moving handles, be careful they don't supinate the wrists at the end of each pulling action. Such supination can cause excess stress on the elbow joint and lead to inflamed forearm muscles.
Of all the resistance machines made, the low-back machine is the most important and potentially the most effective, if used properly. The key to correct technique in this exercise is securing the two leg belts. The purpose of the leg belts is to maintain a stable hip position throughout the exercise, thereby preventing hip extension. This is essential for emphasizing the lower back (spinal erector) muscles, which is clearly the purpose of the low-back exercise. As you watch your client perform the extension movement, all of the action should occur above the hip bones in the lumbar spine area. Make sure your client's head remains in a neutral (straight neck) position throughout the exercise, and that the arms are folded across the chest, so that the upper body moves as a single/stable unit.
Most abdominal machines offer two options with respect to feet position. Your clients may place their feet in front of the footpads, or they may secure their feet behind the footpads. Either way is acceptable, but there is a difference in the muscle emphasis depending on whether the feet are free or secured behind the footpads. When the feet are secured behind the footpads, there is an anchoring effect that maximizes involvement of the hip flexor muscles (rectus femoris, iliacus, psoais groups). When the feet are free, there is less involvement of the hip flexor muscles. In both cases, the rectus abdominis muscles receive an excellent training effect, assuming enough resistance is engaged to cause momentary muscle fatigue within the anaerobic energy system (e.g., 10 to 15 controlled repetitions). Let your clients know that feet-free actions place more emphasis on the trunk flexor muscles, whereas feet-secured actions involve both the trunk flexors and the hip flexors.
The rotary torso exercise works the internal and external oblique muscles that provide so much support and stability for the midsection of the body. The rotary torso machine is typically performed with both arms behind the movement pads. However, only one arm is actually providing force for moving the armature. Have clients pull the left movement pad with the left arm and push the right movement pad with the right arm, thereby putting approximately equal force on both sides of the body. This enables the spine to remain relatively straight and vertical throughout the exercise, thereby placing less stress on the vertebral column, and reducing the injury risk of this highly effective exercise.