Quantitative assay of electromyograms during mastication in domestic cats ( Felis catus )

Mastication has been studied by cinematography with synchronized electromyography (computer quantified and analyzed), while unanesthetized, freely feeding cats ( Felis catus ) were reducing equivalent-sized chunks of raw and cooked beef and cooked chicken. Cats reduce food on one side at a time, and their chewing cycles show both horizontal and anteroposterior deflections. Food objects are shifted from side to side by lateral jerks of the head and movements of the tongue. During the opening phase, the lower jaw is rotated relatively straight downward, and the digastric muscles are active in bilateral symmetry. Near the end of opening, the head jerks upward, both zygomaticomandibulares start to fire, and opening acceleration of the mandible decreases. Closing starts with horizontal displacement of the mandibular canines toward the working side, accompanied by asymmetrical activities from the working side deep temporalis and the balancing side medial pterygoid, as well as a downward jerk of the head. As closing proceeds, the mandibular canines remain near the working side and the working side zygomaticomandibularis and deep masseter are very active. Near the end of closing, the mandibular canine on the working side moves toward the midline, and adductors, digastrics, and lateral pterygoids of both sides are active. The adductors of the working side are generally more active than those of the balancing side. During a reduction sequence, the number and shape of the masticatory cycles, as well as movements of the head, during a reduction sequence are affected significantly by food type. As reduction proceeds, the duration of bite and the muscular activity (as characterized by number and amplitude of spikes) change significantly among muscles of the working and balancing sides. The adductors of the working side are generally most active when cats chew raw beef, less for cooked beef, and least for cooked chicken. In general, the adductor activity reflects food consistency, whereas that of the digastrics and lateral pterygoids reflects more the vertical and lateral displacements of the mandible. Statistical analysis documents that the methods of electrode insertion and test give repeatable results for particular sites in different animals. Thus, it should be possible to compare these results with those produced while other mammalas are masticating.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50273/1/1051630304_ftp.pd

Mastication in the tuatara, Sphenodon punctatus (reptilia: Rhynchocephalia): Structure and activity of the motor system

The masticatory pattern of Sphenodon punctatus , the sole remaining rhynchocephalian, now restricted to islands off the coast of New Zealand, has been analyzed by detailed anatomy, cinematography, cinefluoroscopy, and electromyography. Food reduction consists of a closing, crushing bite followed by a propalineal sliding of the dentary row between the maxillary and palatine ones. The large, fleshy tongue can be protruded to pick up small prey, and also plays a major role in prey manipulation. The rotational closing movement of the jaw, supporting the basic crushing movement, is induced by the main adductor musculature. It is followed by a propalineal anterior displacement relying heavily on the action of the M. pterygoideus. The fiber lengths of the several muscles reflect the extent of shortening. The most obvious modification appears in the M. pterygoideus, which contains a central slip of pinnately arranged short fibers that act a period different from that of the rest of the muscle; their action increases the power during the terminal portion of the propalineal phase. This also allows the animal to use its short teeth in an effective shearing bite that cuts fragments off large prey. The action of single cusped dentary teeth acting between the maxillary and palatine tooth rows provides a translational crushing-cutting action that may be an analog of the mammalian molar pattern. However, this strictly fore-aft slide does not incorporate capacity for later development of lateral movement.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50277/1/1051710307_ftp.pd

The effect of static stretch and warm-up exercise on hamstring length over the course of 24 hours.

STUDY DESIGN: Experimental pretest-posttest control design. OBJECTIVES: The purpose of the study was twofold: (1) to determine the lasting effect of static stretch on hamstring length for up to 24 hours and (2) to compare the efficacy of static stretch with and without warm-up exercise on hamstring length. BACKGROUND: Research is limited on the lasting effects of static stretching and is controversial on the combined effects of warm-up activities and static stretching on muscle lengthening. METHODS AND MEASURES: Fifty-six volunteer subjects (ages 18-42 years) with limited bilateral hamstring length were assigned to 1 of 4 groups: (1) warm-up and static stretch, (2) static stretch only, (3) warm-up only, and (4) control. The warm-up was 10 minutes of stair climbing at 70% of maximum heart rate. Static stretch consisted of a single session of three 30-second passive stretches of the hamstring. Hamstring length was measured preintervention and at several intervals postintervention (immediately and then at 15 minutes, 60 minutes, 4 hours, and 24 hours) using the active knee extension (AKE) test. Data were analyzed using a mixed-model analysis of variance. RESULTS: The warm-up-and-static-stretch group and the static-stretch-only group showed a significant increase in hamstring length between preintervention and all postintervention measurements. At 24 hours poststretch, the warm-up-and-static-stretch group had a mean increase of 10.3 degrees (95% confidence interval, 7.7-12.9) and the static-stretch-only group had a mean increase of 7.7 degrees (95% confidence interval, 4.7-10.7) in AKE range of motion (ROM). Both of these groups did show significant decrease (2.9 degrees and 4.0 degrees, respectively) in hamstring muscle length (AKE ROM) at 15 minutes poststretch when compared to immediate poststretch values. The static-stretch-only and the warm-up-and-static-stretch groups did not differ significantly from each other. Control and warm-up-only groups showed no significant increase in hamstring length between preintervention and any of the postintervention measurements. CONCLUSIONS: A significant increase in hamstring length can be maintained for up to 24 hours when using static stretching. Muscle length gains are greatest immediately after stretching and decline within 15 minutes. The addition of a warm-up exercise prior to stretching does not appear to significantly increase the effectiveness of static hamstring stretching