Human Respiratory - Locomotor System Coordination (Research Paper Sample)

Running Head: RESPIRATORY
Human Respiratory- Locomotor System Coordination
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Human Respiratory- Locomotor System Coordination
Introduction
Researchers have investigated respiratory-locomotor coordination from the perspective of focusing only on entrainment between these systems. This approach has been argued as inadequate given the prevalence of variability found between respiratory and locomotory rhythms as well as the importance of variability in the functioning of other physiological systems.
Coupling between locomotion and respiration
The ventilatory response to exercise in humans is well documented. For example, at the onset of exercise such as cycling or running from a rest, the ventilatory rate responds with an immediate increase (fast response) followed by a somewhat slower rise (slow response) until steady state. There have been numerous attempts to uncover the mechanism(s) that control respiration during exercise. With little evidence that a single mechanism controls respiration. Instead, control of respiration is considered to be an integration of many sources of control that can add, subtract, or multiply to give the precise ventilatory rate (McDermott et al., 2002). The primary sources of control that have been identified work over various time-scales. These include the central respiratory drive that originates in the medulla oblongata, parallel activation of limb musculature and spinal respiratory motor neurons by central motor commands (feed-forward), central and peripheral chemoreflex, neural modification (short-term potentiation), as well as afferent signals from moving limbs. Although various researchers have identified these mechanisms, the extent to which each regulates a ventilation it is still controversial.
Human locomotor-respiratory coordination
The extent to which these coupling mechanisms affect respiration in humans is still unknown. Because of our bipedal locomotion and upright posture, however, we are not forced into 1:1 couplings and locomotion is normally not thought of as interfering with ventilation. A wide range of frequency couplings between respiratory rhythms and movement which has been observed in humans, including coupling ratios of 1:1, 2:1, 3:1, 3:2, 4:1, and 5:2, with the 2:1 ratio being used most often (McDermott et al., 2002).
Although humans appear to have greater variability in respiration during locomotion, there is still evidence of entrainment occurring to varying degrees. It has been suggested that tighter coordination between limb rhythms and respiration may reduce the metabolic cost of a movement, or at least the perception of the workload (Bonsignore et al., 1998).
In the light of this, several researchers have investigated the coordination between locomotory and respiratory rhythms to assess if entrainment increases the economy of movement. In these studies, the level of coordination is intentionally increased above normal spontaneous breathing conditions by pacing breathing to the movement rhythm. Comparisons of the total body VO2 between paced and spontaneous breathing conditions suggest that greater entrainment may reduce the metabolic cost of cycling, but not significantly while walking (van Alphen and Duffin, 1994) or run (Bernasconi and Kohl, 1993).
The effect of entrained breathing on the ventilatory efficiency has been studied during locomotion. Takano and Deguchi (1997) reported that changes from non-competitive female cyclists. Bonsignore et al. (1998) reported that ventilatory efficiency in a group of trained triathletes was slightly greater in entrained breathing than non- entrained breathing during cycling and running during an increasing grade work test compared to an increasing speed work test. These studies suggest that whether entrainment is beneficial in terms of the energetic cost or not may be partly dependent on the training history of the subjects. However, given the fact that entrainment sometimes increases oxygen cost and the sensation of breathlessness during paced and spontaneous breathing, it seems likely that the proposed mechanical constraints do not impose a strong effect on respiration, and that a certain amount of variability between these rhythms is necessary for efficient movement. This speculation is consistent with the fact that in much of the literature investigating the coordination between breathing and locomotion; there are reports that occurrences of entrainment are often variable and intermittent (Takano and Deguchi, 1997).
Postural Control and Respiration
The control of posture is an important ongoing task during many activities including locomotion. This is a significant component of the overall stability of gait because the distribution of body mass is such that two-thirds of the mass is in the upper body (head, arms, and trunk or HAT), which is positioned about two-thirds of body height above the ground (Van Emmerik et al., 2002). Biomechanical research of gait has often treated the upper body as a single, HAT segment that needs to be balance on a moving joint (hip joint in the sagittal plane) (Van Emmerik et al., 2004). Research focusing on the upper body segments particularly the pelvis and trunk, has shown that the upper body is not a single-passive segment, and that the individual segments play an active role in maintaining stable gait (McGibbon and Krebs, 2001).
The integration of respiration and postural control has not been considered in assessments of gait stability despite the fact that researchers have revealed several muscle groups that are involved in both postural control and respiration. Integration of postural and respiratory activity has been identified in the intercostals muscles, the diaphragm, and transverse abdominis (Hodges and Gandevia, 2000). The primary mechanism by which respiratory musculature is thought to stabilize the trunk against perturbations is through an increase in the intra-abdominal pressure, which is achieved by simultaneous contraction of the diaphragm, abdominal and pelvic floor muscles (Hodges et al. 2001). Evidence for this stabilizing strategy is observed when posture was challenged by a single (Hodges et al., 1997) and repetitive (Hodges and Gandevia, 2001) rapid movement of the upper limb. In both cases, the electromyography (EMG) activity of the diaphragm increased just prior to the postural perturbation, consistent with an anticipatory postural response. During the repetitive perturbation, where respiratory activity has to be maintained, postural control and respiration were accomplished by an increase in tonic activity of both the diaphragm and transverse abdominis with superimposed phasic activity modulated at the frequencies of both respiration and postural perturbation. In order to maintain intra-abdominal pressure to stabilize the trunk, the phasic activity associated with respiration in the diaphragm was out of phase with that of the transverse abdominis. These findings have implications for the study of upper body control during locomotion, where there are periodic perturbations to the upper body in all three planes of motion. Locomotion clearly in...