Cervical Joint Position Sense in Hypobaric Conditions: A Randomized Double-Blind Controlled Trial.

Well-adapted motor actions require intact and well-integrated information from all of the sensory systems, specifically the visual, vestibular, and somatosensory systems, including proprioception. Proprioception is involved in the sensorimotor control by providing the central nervous system with an updated body schema of the biomechanical and spatial properties of the body parts. With regard to the cervical spine, proprioceptive information from joint and muscle mechanoreceptors is integrated with vestibular and visual feedback to control head position, head orientation, and whole body posture. Postural control is highly complex and proprioception from joints is an important contributor to the system. Altitude has been used as a paradigm to study the mechanisms of postural control. Determining the mechanisms of postural control that are affected by moderate altitude is important as unpressurized aircrafts routinely operate at altitudes where hypoxia may be a concern. Deficits in motor performance arise when the reliance on proprioceptive feedback is abolished either experimentally or because of a disorder. As pilots require good neck motor control to counteract the weight of their head gear and proprioceptive information plays an important role in this process, the aim of this study was to determine if hypoxia at moderate altitudes would impair proprioception measured by joint position sense of the cervical spine in healthy subjects. METHODS: Thirty-six healthy subjects (Neck Disability Index < 5) volunteered to participate. Neck position sense was evaluated using a three-dimensional motion analyzer. To create the environment, a hypobaric chamber was used to simulate artificial moderate altitude. Head repositioning error was measured by asking the subject to perform a head-to-neutral task after submaximal flexion-extension and right/left rotation movements, and a head-to-target task, in which the subjects had to return to a 30° right and left rotation position. FINDINGS: Exposure to artificial acute moderate altitude of 7,000 feet had no significant effects on cervical joint position sense measured by head repositioning accuracy in healthy subjects. Discussion/impact/recommendations: Postural control mechanisms are very sensitive to acute mild hypoxia and have been recently investigated. Acute hypobaric hypoxia at moderate and high altitudes has a negative effect on postural control. However, which part of the postural system is affected has not yet been determined and proprioception has been little investigated. The results from this study highlighted that in healthy subjects with good cervical spine proprioception at baseline, artificial hypoxia induced by the simulation of moderate altitude does not increase head repositioning error. Further studies should investigate cervical joint position sense in real aircraft, at different altitudes and in a group of experienced helicopter pilots, to evaluate the impact of moderate altitude on cervical joint position sense in a different population. Conducting the same experiments in a population of pilots and in real flight conditions should be considered, since various factors such as the level of proprioception, head posture, type of movement, head load, muscle fatigue, flight altitude, and the length of flight time might influence the kinesthetic sensitivity.

Sedentary behaviour, physical activity and a continuous metabolic syndrome risk score in adults.

OBJECTIVE: The association of sedentary behaviour and leisure time physical activity with a validated continuous metabolic syndrome risk score was investigated in adults. SUBJECTS/METHODS: A number of 992 adults (559 men) without cardiovascular disease or diabetes. Subjects reported time spent in leisure time physical activity and television watching/computer activities. A validated metabolic syndrome risk score, based on waist circumference, triglycerides, blood pressure, fasting plasma glucose and high-density lipoprotein cholesterol, was used. The metabolic syndrome risk score and time spent in sedentary behaviour and physical activity were analysed as continuous variables using multiple linear regression. RESULTS: Metabolic syndrome risk was positively associated with time spent watching television/computer activities, irrespective of physical activity level, and after adjustment for age, education level, smoking status and dietary intake in women aged > or =45 years (beta=0.184, P<0.05). Independent of the time being sedentary, moderate to vigorous leisure time physical activity was inversely associated with metabolic syndrome risk in men (<45 years: beta=-0.183, P<0.01; > or =45 years: beta=-0.192, P<0.01) and women aged > or =45 years (beta=-0.203, P<0.01). CONCLUSIONS: Although cross-sectional, the present results support inclusion of efforts to decrease sedentary behaviour in metabolic syndrome prevention strategies for women aged > or =45 years, besides promotion of moderate to vigorous physical activity, since both behavioural changes might show additional effects.

Relationship of obesity with physical activity, aerobic fitness and muscle strength in Flemish adults.

AIM: The aim of this study was to analyse differences in physical activity, cardiorespiratory fitness (CRF) and muscle strength between normal weight, overweight and obese adults and to investigate the role of physical activity variables in the analyses of differences in CRF and muscle strength between these groups. METHODS: A total of 807 men and 633 women (age: 18-75 years) were included in this cross-sectional study. Weight, height, waist circumference (WC) and bioelectrical impedance were measured. Different dimensions of physical activity were assessed using a validated questionnaire. CRF (VO(2peak)) was evaluated by a maximal test on a cycle ergometer. Knee strength was measured with a calibrated Biodex System Pro 3 dynamometer. Three methods were used for classification in obesity groups: body mass index (BMI), WC and combined BMI-WC classification. RESULTS: Health-related sports and physical activity level are negatively associated with obesity in men, but not in women. Television viewing is positively associated with obesity, while VO(2peak)/fat free mass (FFM) and knee strength/FFM show a negative association with obesity in both genders. Overall, subjects with normal WC seem to be more physically active and to have somewhat better values for CRF compared to those with high WC within the same BMI category. Lower values for relative CRF and knee strength in obese subjects compared to their lean counterparts remain after adjustment for physical activity. CONCLUSION: This study confirms the lower level of physical activity and the impaired CRF and knee strength in obese adults compared to their lean counterparts. This study also sustains the importance of measuring WC and CRF during clinical examinations.