The two papers I am reviewing are – “Biomechanical behaviour of muscle-tendon complex during dynamic human movement” – Senshi Fukashiro, Dean C. Day and Akinori Nagano, and “Passive properties of human skeletal muscle during stretch maneuvers” – S. P. Magnusson. The muscle tendon complex and human skeletal muscle are synonymous. These are the muscles that help us create dynamic movements, which includes – jumping, stretching, heel raise exercise. The second article is published in Journal of Medicine and Science in Sports, which speaks for itself that such studies are greatly beneficial for understanding the long term fatigue of the muscle-tendon system. Also, it is essential to discover the various mechanical properties along with the benefits of stretching exercises for the athletes. Such research papers are heavily based on experimental work and can take months for data collection and data analysis. It is hard to recreate the same conditions for each experiment as the specimen (animal or human) cannot be controlled. However, authors have tried to perform some repeated controlled experiments also that will be discusses later. Several experiments have also been done to compare the muscle conditions for youngsters and older people. The study the authors are conducting is based on a 1970 study done where it was suggested that muscoskeletal tightness might be related to the muscle strain, while the loose joints had a higher chance of ligament injury. This idea of flexibility and injury due to its absence (in some essence) is the key basis of these two papers. It is believed that this increased risk of injury can be explained by material properties of the muscles.
As it has been previously accounted, the human body anatomical structures do not behave similarly to the various metallic materials. Similarly, the muscles and tendons do not behave elastically. These muscles demonstrate a viscoelastic behaviour with three regions – toe region, a transition period and a linear portion. In the experimental set up, the author measures the y-axis in terms of dynamic torque. Y-axis is generally force, however, measuring the force on the muscles is a complex phenomenon. As suggested in the caption of the figure, this is equivalent to stiffness. The axis represents the strain or change in position in terms of angles (radians). This diagram is synonymous to that of various metallic materials. Area under the curve represents the energy released by the muscle. Because these muscle are so “soft,” at the very beginning, the muscles strain without any application of force. No energy is released during this period. As Dr. Babu talked about in her talk, this is the region where the collagens are straightening. It is similar to stretching loose skin. This section is known as the toe region. Following this is the transition phase. By this region, the collagens and elastic fibers have started stretching. Since the torque is acting on multiple fibers at the same time, the strain that takes place is not linear. In the final region, the collagen and elastin fibres start experiencing fracture. Fukashiro suggests to create a stress-strain curve using the computer simulation since ethical and technical issues arise with the proposed methods. Computer simulations have truly helped us further our understanding on many of these muscles along with experimental results. These muscles and tendons do not behave like a perfect spring, but both possess mechanical properties that can be described briefly by relatively simple elastic models for each section. From this experiment, animal models have shown that biological materials respond in a non-linear fashion, however, this has not been confirmed in a human model.
These papers suggest several key findings of incredible importance. They suggest that flexibility is extremely important in discovering the behaviour of muscle fatigue when humans make stretch – shortening cycles. This is something similar to what Dr. Samaan was looking at but at the hip. These quick motions resembles when an athlete has to immediately change directions or deceive the opponent. Dr. Samaan mentioned that this is where most of the injuries occur and numerous patients are treated annually for similar problems. This kind of injury is tests the body’s flexibility and therefore, learning about the proper stretching or exercises that prevent this is of keen interest. The mechanical properties of the muscles and tendons become extremely important in such problems.
Another problem that is faced in any biological testing is relating the studies done on animals organs or tissues to that of humans. Fukashiro notes that some various mechanical properties such as tendon compliance received from mechanical models provide slightly different values in comparison to that of human studies. However, the basic properties, such as the figure 1, continue to remain the same for human muscles just with different constants. So, in some aspects, the animal based data is relevant, while in other cases there is some discrepancy, and this is the research that needs to be conducted.
The authors here are proposing the actual influence of stretching exercise on short and long term performance. The experimental setup is shown in figure 2. The person is made to sit in the chair as shown and a belt is put around the waist to keep the person stable. One of the thighs is connected to the Electromyogram (EMG). Then the experiment is modified in different ways to facilitate the requirement of the study being conducted. The high is made to rotate at a constant rate and various sensors installed measured the mechanical properties in the muscles through the EMG. The rotation rate, the time period, the positions of sensors can all be changed to the requirement.
Using this experiment, the author was able to reproduce the experiment repetitively. To test this, the subjects were tested with one hour of rest period where the experiment was carried out again. The measurement in terms of stiffness and energy did not differ in both the experiments. This is an important finding because this means that if the fatigue stage is not reached in the elastic and collagen, they will come back to the original state (one hour) after the experiment. This is something that Dr. Babu also talked about, where the collagen returns to the unstretched conditions after loading. This study also concluded that different kinds of studies can be carried out on the same specimen if the muscle is allowed to rest for an hour. The article further on goes to discuss the single stretch, repeated stretches, stretching techniques and long term flexibility training, along with various effects of strength training. The other paper is geared more towards the computational side with ultrasonography. This paper by Fukashiro proves that computationally, getting access to various biomechanical variables is much easier than through various experimental procedures, as discussed in the paper by Magnusson.
Ofcourse, a combination of both the fields is required to find a balance in the field. For example, Dr. Chengkai Dai mentioned the importance of a collaboration between the hearing and balancing ear teams. He also recognised the importance of a comprehensive finite element model combining both the sides of the ear, while at the same time, he wants to continue testing at OUHSC. The two papers discussed introduce two method of going about research.
This reading assignment, once again, helped me learn something that I had not considered before in the field of biomechanics. The most surprising result for me was a quantification of the fact that stretching before exercising leads to a greater agility. As an athlete, I am aware of this but being able to see the experiment for it was really beneficial for my learning. I also liked that in these readings, I was finally able to understand Dr. Samaan’s faculty interview.