DAYTON, Ohio — Sticking to an exercise program can be difficult if you feel you are not making progress quickly enough.

Even if given the same training program, changes in body fat, strength and muscle happen to each of us at different rates. Many factors can affect how the body responds to exercise.

Some of these factors are within our control, such as the frequency and duration of workouts, while others cannot be changed, such as body type and age. Some unchangeable factors include:

Body structure

How we are built, including limb and muscle length, influence our strength levels.

For example, pound for pound, individuals with shorter limbs find many strength-training exercises easier to perform than someone with longer arms and legs due to leverage factors. In other words, the closer the resistance is to the body, the easier it becomes to lift. The further away, the more difficult.

Limb and muscle length varies greatly from person to person and is genetically predetermined. Muscle length influences strength development. Muscle and strength potential is greater for individuals with longer muscles as compared to those with relatively short muscles.

Tendon insertion

Tendons are strong bands of tissue that transmit the force generated by muscular contraction to the bones, resulting in movement at a given joint. The point where the tendon attaches varies from person to person, and affects strength ability.

An example is the biceps muscle, whose function it is to allow for the elbow to bend and the forearm to rotate. The biceps has tendons that attach to the front of the shoulder as well as to the forearm. The further from the elbow joint the forearm tendon attaches, the greater the biomechanical advantage, and the greater the amount of weight lifted.

Age

Another factor we have no control over is age. Into our teens, we experience increased muscle and bone growth naturally. As adults, we must apply stress to the muscles and bones in order for growth to occur or to prevent loss from happening.

Regular resistance training is the best way to help preserve muscle and bone tissue and reduce risk of injury as we get older. Studies have shown that even into our 90s and beyond, muscle size and strength can be improved with exercise.

Muscle fiber type

We are born with different types of muscle fibers, each responding in a different way to exercise.

Type I fibers are recruited when conditions are such that a small amount of force is needed, but for long periods of time. Resistant to fatigue, they are well suited for cardiovascular (aerobic) exercise or with anaerobic (weightlifting) activity when the workout calls for a weaker muscular contraction. Each muscle fiber type contracts at different speeds. Type I muscle fibers are called “slow twitch” because they contract slowly, while type II-A muscle fibers do not produce strong contractions and have minimal capacity for muscle growth.

Type II-B fibers by contrast, produce high levels of force but for short periods of time, and so are best suited for anaerobic activity such as strength training. These fibers are called “fast twitch” because they are quick to contract under heavy weight loads. Although Type II-B fibers contain large amounts of glycogen (energy) for heavier weight lifting workouts, they also fatigue quickly.

For people with muscle-growth goals, these fibers need to be activated to the fullest, and must be provided with proper rest between workouts to fully recover and repair.

Controllable ways to achieve success include: proper form, speed of movement and appropriate weightloads, as well as the duration, frequency and intensity of exercise.