Gordon R. Chalmers

Strength training: Re‐examination of the possible role of golgi tendon organ and muscle spindle reflexes in proprioceptive neuromuscular facilitation muscle stretching

Literature concerning the theoretical role of spinal reflex circuits and their sensorimotor signals in proprioceptive neuromuscular facilitation (PNF) muscle stretching techniques was examined. Reviewed data do not support the assertion commonly made in PNF literature that contraction of a stretched muscle prior to further stretch, or contraction of opposing muscles during muscle stretch, produces relaxation of the stretched muscle. Further, following contraction of a stretched muscle, inhibition of the stretch reflex response lasts only 1 s. Studies examined suggested that decreases in the response amplitude of the Hoffmann and muscle stretch reflexes following a contraction of a stretched muscle are not due to the activation of Golgi tendon organs, as commonly purported, but instead may be due to presynaptic inhibition of the muscle spindle sensory signal. The current view on the complex manner by which the spinal cord processes proprioceptive signals was discussed. The ability of acute PNF stretching procedures to often produce a joint range of motion greater than that observed with static stretching must be explained by mechanisms other than the spinal processing of proprioceptive information. Studies reviewed indicate that changes in the ability to tolerate stretch and/or the viscoelastic properties of the stretched muscle, induced by PNF procedures, are possible mechanisms.Abstract Literature concerning the theoretical role of spinal reflex circuits and their sensorimotor signals in proprioceptive neuromuscular facilitation (PNF) muscle stretching techniques was examined. Reviewed data do not support the assertion commonly made in PNF literature that contraction of a stretched muscle prior to further stretch, or contraction of opposing muscles during muscle stretch, produces relaxation of the stretched muscle. Further, following contraction of a stretched muscle, inhibition of the stretch reflex response lasts only 1 s. Studies examined suggested that decreases in the response amplitude of the Hoffmann and muscle stretch reflexes following a contraction of a stretched muscle are not due to the activation of Golgi tendon organs, as commonly purported, but instead may be due to presynaptic inhibition of the muscle spindle sensory signal. The current view on the complex manner by which the spinal cord processes proprioceptive signals was discussed. The ability of acute PNF stretching procedures to often produce a joint range of motion greater than that observed with static stretching must be explained by mechanisms other than the spinal processing of proprioceptive information. Studies reviewed indicate that changes in the ability to tolerate stretch and/or the vis‐coelastic properties of the stretched muscle, induced by PNF procedures, are possible mechanisms.

Can fast-twitch muscle fibres be selectively recruited during lengthening contractions? Review and applications to sport movements

Literature examining the recruitment order of motor units during lengthening (eccentric) contractions was reviewed to determine if fast-twitch motor units can be active while lower threshold slow-twitch motor units are not active. Studies utilizing surface electromyogram (EMG) amplitude, single motor unit activity, spike amplitude–frequency analyses, EMG power spectrum, mechanomyographic, and phosphocreatine-to-creatine ratio (PCr/Cr) techniques were reviewed. Only single motor unit and PCr/Cr data were found to be suitable to address the goals of this review. Nine of ten single motor unit studies, examining joint movement velocities up to 225°/s and forces up to 53% of a maximum voluntary contraction, found that the size principle of motor unit recruitment applied during lengthening contractions. Deviation from the size principle was demonstrated by one study examining movements within a small range of low velocities and modest forces, although other studies examining similar low forces and lengthening velocities reported size-ordered recruitment. The PCr/Cr data demonstrated the activation of all fibre types in lengthening maximal contractions. Most evidence indicates that for lengthening contractions of a wide range of efforts and speeds, fast-twitch muscle fibres cannot be selectively recruited without activity of the slow-twitch fibres of the same muscle.

Strength training: Do Golgi tendon organs really inhibit muscle activity at high force levels to save muscles from injury, and adapt with strength training?

Abstract Introductory textbooks commonly state that Golgi tendon organs (GTOs) are responsible for a reflex response that inhibits a muscle producing dangerously high tension (autogenic inhibition). Review of the relevant data from animal studies demonstrates that there is wide variability in the magnitude of, and even the presence of, GTO autogenic effects among locomotor hindlimb muscles, and that data on GTO effects under conditions of voluntary maximal muscle activation are lacking. A single available study on GTO function in humans, during a moderate contraction, surprisingly shows a reduction in autogenic inhibition during muscle‐force production. Further, it is not possible to find experimental evidence supporting the idea that strength training may produce a decrease in GTO mediated autogenic inhibition, allowing greater muscle activation levels and hence greater force production.

Effect on performance of learning a pilates skill with or without a mirror

Mirrors are often used in an instructional environment where precise movements must be learned (e.g., martial arts, Pilates, dance). The potential for mirrors in the learning environment of a Pilates class, to affect the subsequent performance of a Pilates star movement when mirrors are not present, was examined. Twenty subjects learned the Pilates star movement over seven weeks, either with (n=11) or without (n=9), mirrors present in the Pilates studio. Performance of the star without mirrors present was assessed quantitatively before and after the training, by video analysis of the degree of lateral straightness of the subjects body at the start, middle, and end of the star movement. Performance of the star movement without a mirror present improved similarly for both the group that learned with, and the group that learned without, mirrors present (p<0.05). These results indicate that the inclusion of mirrors in a learning environment, to provide immediate visual feedback during learning, does not necessarily enhance the subsequent performance of a skill when mirrors are not present.

Kinesio Tape and Shoulder-Joint Position Sense

CONTEXT Joint position sense (JPS) is a key neuromuscular factor for developing and maintaining control of muscles around a joint. It is important when performing specialized tasks, especially at the shoulder. No researchers have studied how Kinesio Tape (KT) application affects JPS. OBJECTIVE To investigate the effects of KT application and no tape on shoulder JPS at increasing shoulder elevations in athletes. DESIGN Cross-sectional study. SETTING University laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 27 healthy athletes who did not participate in overhead sports (age = 20.44 ± 1.05 years, height = 175.02 ± 11.67 cm, mass = 70.74 ± 9.65 kg) with no previous pathologic shoulder conditions volunteered for the study. All participants were from 1 university. INTERVENTION(S) Shoulder JPS was assessed at increasing elevations with and without KT application. Participants attempted to actively replicate 3 target positions with and without the KT and without visual guidance. MAIN OUTCOME MEASURE(S) We examined absolute and variable repositioning errors at increasing shoulder-elevation levels with and without KT application. RESULTS Data revealed an interaction between tape and position for absolute error (F2,52 = 4.07, P = .02); simple effects revealed an increase in error, with KT demonstrating a 2.65° increase in error at 90° of elevation compared with no tape (t26 = 2.65, P = .01). The effect size was medium (ω(2) = .135). Variable error showed no interaction of tape and position (F2,52 = .709, P = .50). Further analysis of simple effects was not needed. However, we still calculated the effect size and observed small effect sizes for tape (ω(2) = .002), position (ω(2) = .072), and tape by position (ω(2) = .027). CONCLUSIONS At 90° of elevation, shoulder JPS was impaired by the application of KT.

Responses of human motoneurons to high-frequency stimulation of Ia afferents.

This study was designed to extend to humans the findings of classical studies on anesthetized cats, which have examined the discharge of spinal motoneurons in response to high‐frequency stimulus trains delivered to Ia afferents. Experiments were conducted on the monosynaptic pathway in the flexor carpi radialis (FCR) and soleus muscles. Subjects maintained a rhythmic discharge of a single motor unit (SMU) in either the FCR or soleus while homonymous Ia afferents were stimulated with either a single‐ or multipulse train. An n@IPI stimulus train had n pulses (n = 2–4) and an interpulse interval (IPI) of 1–8 ms. For each condition and motor unit, surface electromyographic (EMG) activity was averaged, and peristimulus–time histograms (PSTHs) were constructed for the SMU. The magnitude of the EMG was high for IPI = 1 ms, low for IPI = 2–3 ms, and high for IPI = 4–8 ms. SMU responses showed a similar pattern, which indicated that the increased EMG response was due to the presence of multiple peaks in a PSTH. The key results indicate that: (1) a short, high‐frequency stimulus train enhances the discharge probability of a motoneuron above that observed with a single pulse; and (2) the increased motoneuron responses are significantly greater for the FCR than for the soleus muscle.

Common errors in textbook descriptions of muscle fiber size in nontrained humans.

Exercise science and human anatomy and physiology textbooks commonly report that type IIB muscle fibers have the largest cross-sectional area of the three fiber types. These descriptions of muscle fiber sizes do not match with the research literature examining muscle fibers in young adult nontrained humans. For men, most commonly type IIA fibers were significantly larger than other fiber types (six out of 10 cases across six different muscles). For women, either type I, or both I and IIA muscle fibers were usually significantly the largest (five out of six cases across four different muscles). In none of these reports were type IIB fibers significantly larger than both other fiber types. In 27 studies that did not include statistical comparisons of mean fiber sizes across fiber types, in no cases were type IIB or fast glycolytic fibers larger than both type I and IIA, or slow oxidative and fast oxidative glycolytic fibers. The likely reason for mistakes in textbook descriptions of human muscle fiber sizes is that animal data were presented without being labeled as such, and without any warning that there are interspecies differences in muscle fiber properties. Correct knowledge of muscle fiber sizes may facilitate interpreting training and aging adaptations.

Exercise Information Resources on the World Wide Web

Abstract Health professionals and members of the public are often interested in locating exercise information on the World Wide Web (the Web). There is a large amount of information available on the Web; however, the challenge for all people is to identify the high quality information that can be depended upon. Much of the quality exercise information on the Web is hidden within sites of reputable organizations concerned with exercise and health. This article examines several categories of commonly needed exercise related information. For each category, a few high quality sources of exercise information are listed. Combined, these Web sites provide an excellent and extensive body of knowledge for a person who is not experienced with exercise and wants to get started learning, or for a person with a moderate level of experience and knowledge who wants to learn more.

Shoulder elevation affects joint position sense and muscle activation differently in upright and supine body orientations.

OBJECTIVE Investigate the effects of shoulder elevation on repositioning errors in upright and supine body orientations, and examine these effects on anterior and posterior deltoid muscle activation. We hypothesized decreased errors, and altered anterior and posterior deltoid activation with increasing elevation, in both orientations. DESIGN Crossover trial. SETTING University laboratory. PARTICIPANTS Thirty-five college-aged participants. INTERVENTION Subjects attempted to replicate target positions of various elevation angles in upright and supine body orientations. Also, anterior and posterior deltoid activation was recorded in each shoulder position and body orientation. MAIN OUTCOME MEASURES Vector and variable repositioning errors, anterior and posterior deltoid percentage of maximal contraction. RESULTS Vector error was greater in supine compared to upright at 90° and 110°, but not at 70°. Variable error was larger in supine than upright, but was unaffected by elevation. Anterior deltoid activation increased with elevation in the upright posture only. Posterior deltoid activation increased with elevation across postures. CONCLUSIONS Muscle activation, external torque, and cutaneous sensations may combine to provide afferent feedback, and be used with centrally-generated signals to interpret the state of the limb during movement. Clinicians may prescribe open kinetic chain exercises in the upright posture with the shoulder elevated approximately 90-100°.