180 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. • Sideways motions occur in the frontal plane. • Rotational movements occur in the transverse plane. The frame of reference for all movement is the anatomical position. In this position, the human body is erect with the hands at the sides and the palms facing forward. As you read this section, refer to the illustrations in Figure 6.12. Movements in the Sagittal Plane The primary movements within the sagittal plane are flexion, extension, and hyperextension. Flexion describes forward-bending motion of the head, trunk, upper arm,forearm,hand,andhip.Flexionalsoincludes backward motion of the lower leg at the knee. In flexion movements, body surfaces are coming together. Extension returns body segments from a position of flexion to the anatomical position. Hyperextension continues the extension motion past the anatomical position. Directional Motions Skeletal muscles have attachments at both ends the most common attachments are tendon connections to bone. The end of a muscle that attaches to a relatively fixed structure is called the origin. The end of a muscle that attaches to a bone, which typically moves when the muscle contracts, is called the insertion. For an example of origin and insertion, consider the brachialis muscle, which crosses the anterior side of the elbow. Its origin is on the humerus, and its inser- tion is on the ulna in the forearm. When the brachialis contracts, the forearm (ulna) is pulled toward the upper arm while the upper arm (humerus) remains stationary. Remember—when stimulated to develop tension, muscles can only pull. They are incapable of pushing. In addition, remember from Chapter 1 that three major planes through the center of the body are used to describe the human body and its movements: • Forward and backward motions take place in the sagittal plane. Strength Training Over the past several decades, a growing body of research has led to progressively more sophisticated knowledge about strength training techniques. It is well documented that strength can be increased through regular resistance training. The resistance can be anything that resists the action of contracting muscles. Doing calisthenics, lifting weights, or shoveling snow all qualify. However, body weight exercise, isolation exercise (involving motion of only one joint), plyometric exercise (involving eccentric contraction followed immediately by concentric contraction), unilateral exercise (involving only one side of the body), and kettlebell training all appear to be limited in their potential to increase maximal strength. With weightlifting, strength is best improved by lifting relatively heavy weight for relatively few repetitions and progressively increasing the amount of weight lifted over time. One popular protocol, for example, involves doing two sets of 12 repetitions three times per week. Given an appropriate resistance level, multiple sets produce superior training benefits compared to a single set for a given exercise. The optimal distribution of strength training sessions over a week remains a topic of debate, however. In a recent study with 290 military conscripts, one group was assigned 15 minutes of strength training four times per week, while another group trained for 60 minutes once a week. At the end of the nine-week experimental period, there were no significant differences in strength gains between the groups. This suggests that for a given total duration of training in a week, the distribution of the training time over the week is not consequential. However, there is also evidence that training time distribution is important for certain groups, especially when the goal of training extends beyond increasing strength. For example, in a review of the scientific literature on strength training in hypertensive individuals, training fewer than three times per week was found to be less effective in lowering blood pressure than more frequent training. A study of progressive resistance training in 11-year-old children with type 1 diabetes found that with training sessions twice a week, a minimum of 32 weeks of training was required to produce a significant reduction in blood glucose. Topics that remain under investigation include the efficacy of various protocols with eccentric strength training, variable resistance training, and programming that combines heavy and light loads. Whereas resistance training is normally performed with slow, controlled movements to ensure muscle activation throughout the range of motion, for athletes training for power, as well as strength, it is also necessary to incorporate protocols involving fast movement speeds. Well-documented benefits of regular strength training for everyone include increasing muscle mass, increasing bone density, improving balance and neuromuscular coordination, increasing basal metabolic rate, lowering blood pressure, and decreasing body fat. A reduction in spasticity with eccentric training has also been observed in patients with multiple sclerosis. Research Notes