Another way that pathokinematics, or movement that falls outside the norm can impact performance is by increasing the amount of energy required to move the body in order to perform the function or participate in the sport. If the system is working properly, the limbs are controlled easily and efficiently and the least amount of energy is used to move the body---to walk or run. However, simple tightness or weakness in any part of the body can have a dramatic effect on the quality and efficiency of movement and therefore the energy required to move a certain distance within a certain amount of time. This is often seen when there is hip flexor tightness. During the running cycle, one of two things happens. They shorten their stride length to compensate for the tightness (makes running less efficient) or they rotate in their lumbar spine to make up for the lost motion (which can lead to low back pain).
Of course if natural stride length is shortened, as in the walking/running example, it also takes more steps to travel the same distance, and consequently more energy. This lost energy cannot then be used to extend the time of exercise or the speed of leg turnover in running or walking. Sometimes, only one hip flexor is tight, which can cause the stride length to be asymmetrical. Such asymmetry also decreases the efficiency of movement, and again more energy is required to travel the same distance. So, it is not only more difficult to move when moving the body in “unusual” ways, but it also takes longer to move the body the same distance at any given speed. Both the increased difficulty and the increased length of time it takes to move require additional energy expenditure.
Muscular endurance is defined as the ability of a muscle or group of muscles to sustain repeated contractions against resistance for a sustained period of time. Factors that influence endurance are:
Improvements in the first two factors come with endurance, power and cardiovascular training. However, improvement in exercise economy (which is impacted by the quality of movement) has a direct effect on efficiency and consequently, energy conservation. In the walking/running example above a simple improvement in stride length can result in improved efficiency of the movement and entire system, leading to less energy expenditure, which results in improved athletic endurance---in this case, the ability to run for a longer period of time before having to stop. This is where a good running assessment and orthopedic assessment come into play. Getting someone who knows not only how to assess your running gait but also performing a detailed orthopedic exam to see where the limitations are that may be leading to your altered running gait.
Power and Speed
Power is defined as the rate of work being done per unit of time. In athletics, we calculate power equal to force over time (P = F/T) or the amount of time that it takes to move an object (a weight, sled, bike or your body weight) a given distance. Power can be increased by either increasing the amount of force applied or by reducing the amount of time it takes to move the object. So, improvement in power output can be influenced in two ways: increasing force or decreasing time.
To explain this, we must first talk about muscles and specifically, length and tension relationships.
Muscles work in a length and tension relationship. There are optimal lengths at which muscles produce the maximum amount of force (see the graph above). If a muscle is in a position that is shorter or longer than this optimal position, then the strength or force that the muscle can produce is decreased. Take for example, the bicep curl exercise. When someone performs a bicep curl, there are stages during the motion that the exercise is more or less difficult. Typically greater effort is required at the beginning of the curl and at the end of the curl. Your bicep is strongest in the mid-range of the motion, and so it is at this point that the least amount of energy is required to move the weight or curl the arm upward. It is at this point that the tension the muscle is able to produce is at its highest, relative to its length, and therefore this is the optimal range of motion in which the bicep can produce the most force.
This same concept carries over to all other body movement. Abnormal movement patterns or pathokinematics move the body, including all its joints, ligaments, tendons and muscles outside the “optimal” range. Length/tension relationships in the muscles are drastically altered when we move abnormally and consequently, less force can be produced by the muscles. To illustrate this point, let’s take a look at the following example.
Performance tests such as the vertical jump and 40 yard dash show a marked deterioration as compared to his pre-injury results. He has been performing squats as a part of his rehabilitation and training routine in order to strengthen the injured limb and thereby improve his performance results. However, he is having difficulty understanding why he continues to have such a large strength deficit on the left side. When we view his squat, it is apparent to even the casual observer that there are several issues that might contribute to such a strength deficit on the left side and the resulting decrease in performance on these performance tests as well as on the football field.
When we consider length/tension relationships, we know that if asymmetrical movement patterns like the one seen in this photograph are not corrected, none of this athlete’s muscles from the lower back down will ever be as strong as they could be, nor will they be able to produce as much power as they would in a more symmetrical movement pattern. Part of his overall weakness is actually the result of weakness in his right side as well as his left. The right, in this example, will always be worked more than the left due to the marked weight shift to that side, which obviously causes more of the load burden to be borne on that side. However, because there is also a dramatic change in the length tension relationship on that side, the right side will never be as strong as it would be either if the exercise was performed correctly. Because of the high degree of shift, his left quadriceps is put in a lengthened position while the right is in a shortened position. His left gluteus medius and maximus are put in lengthened positions and his right in shortened positions. So, as stated before, even though his right might be stronger, it will not be as strong as it could be until these length/tension relationships are corrected and the athlete is able to access and use the ranges in which his muscles can produce the maximum amount of force.