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Following preliminary indications that in some individuals arm exercise enhanced rather than reduced simultaneous leg endurance, ten young men and women performed three forms of intermittent work to volitional exhaustion, under duty cycles of 45 s work, 15 s rest. The protocols were as follows: (A) knee extensions at 30% maximum voluntary contraction (MVC); (B) 30% MVC knee extensions combined with arm cranking at 130% of their own lactate threshold; (C) combined 30% MVC knee extensions and arm cranking at 20% of their own lactate threshold. Heart rate, oxygen uptake (VO(2)), and blood lactate concentration were among the variables recorded throughout. All physiological indicators of demand were substantially higher in protocol B than in protocols A or C [heart rate: (A) 154 beats . min(-1), (B) 171 beats . min(-1), (C) 150 beats . min(-1); VO(2): (A) 11.9 ml . kg(-1) . min(-1), (B) 21.7 ml . kg(-1) . min(-1), (C) 14.2 ml . kg(-1) . min(-1); blood lactate concentration: (A) 3.3 mmol . l(-1), (B) 5.1 mmol . l(-1), (C) 2.8 mmol . l(-1)], yet there were no significant differences (P > 0.05) in the endurance times between the three conditions [(A) 11.43 min, (B) 11.1 min, (C) 10.57 min] and seven participants endured longest in protocol B. Results from protocol (C) cast doubt on explanations in terms of psychological distraction. We suggest that lactic acid produced by the arms is shuttled to the legs and acts there either as a supplementary fuel source or as an antagonist to the depressing effects of increased potassium concentration. 相似文献
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OBJECTIVE: To determine which areas of family functioning lay therapy intervention can improve in a home visitation program for first time mothers at high risk for parenting difficulties, including the potential for child abuse and neglect. METHODS: Families were assessed for risk of parenting difficulties using the Parent Readiness and Risk Assessment Checklists. Lay therapists completed the Scale of Family Functioning pre- and postintervention with 108 high risk families for whom they provided support, education, and referrals. RESULTS: Paired t tests were done to determine whether the eight categories of the Scale of Family Functioning improved from baseline to termination of the service. Four categories showed statistically significant improvement: social support (p = .001), self-esteem (p < .001), confidence as a parent (p < .001), and affective relationships (p = .003). CONCLUSIONS: Statistically significant improvement occurred in four of the eight categories on the Scale of Family Functioning indicating that home intervention programs can improve some categories of family functioning. Longer intervention and an increased focus on improving parent/infant interactions may be able to increase parental sensitivity and expectations. In this study, the categories of family conflict and stability/meeting basic needs were not amenable to change with lay therapy intervention. 相似文献
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Abstract Three modern views about the factors limiting oxygen uptake in healthy humans are set against the original (early 1920s) concept of A. V. Hill and colleagues. The majority view for most of the intervening time has been that cardiac output is the essential limiting function. Among recent research in support of this contention is that, in quadrupeds, pericardiectomy, which allows greater diastolic filling, elevates maximum oxygen uptake; however, the relevance to bipedal exercise can be questioned. In any case, algebraic analyses of model systems indicate that all identifiable stages on the oxygen transport pathway, from pulmonary diffusion to oxidative phosphorylation in skeletal muscle mitochondria, materially influence maximum uptake. Thus, if a high cardiac output is to be of benefit, all the other steps must function better too. Nevertheless, these two viewpoints concur that the limit to maximum oxygen uptake is somatic. In contrast, there are strong indications that at altitudes where oxygen availability is about half that at sea level, cerebral oxygenation is a limiting factor, and some recent experiments raise the possibility that it might be a substantial influence at sea level also. Clearly, consensus cannot yet be reached on the question posed in the title. 相似文献
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Hiking physiology and the "quasi-isometric" concept 总被引：1，自引：0，他引：1
Spurway NC 《Journal of sports sciences》2007,25(10):1081-1093
The literature indicates that the heart rate of a planing-dinghy sailor, in winds of 4 - 5 m . s(-1), is in the range seen in aerobic athletes, yet oxygen consumption (VO(2)) is roughly half that of the same individual cycling at that heart rate. Thus, although upper-body dynamic activity is a contributing factor, the dominant physiological demand must be the "quasi-isometric" stress on the lower-body anterior muscles - especially the quadriceps, which appears to impose 40 - 50% of the total oxygen demand in a typical hiking posture. Therefore, a non-trivial part of the sailor's fitness training should involve sustained quadriceps stress. Estimates of this stress on water vary widely in the literature, but about 25 - 30% maximal voluntary contraction (MVC) tallies with endurance times recorded both in the literature and in an outline of new work reported here. Muscle blood flow is restricted under such a load, but not occluded. Laser Doppler measurements of femoral blood flow on a leg-extension ergometer found similar values during 10 - 30% MVC, much less at 40%, and marked hyperaemia on relaxation from 20% MVC or more - implying metabolic debt. Adding low-amplitude alternating leg movements while holding the same overall load stationary, and therefore increasing only internal not external work, further elevates blood flow and VO(2) both during and after exercise. Femoral-vein lactate concentration is also higher after these movements. Speculations that unusually dynamic lower-body movements by elite sailors might assist hiking endurance are not supported by these findings. Nevertheless, afloat or ashore, capillary lactate concentrations hardly ever exceed 5 mmol . l(-1), even during the post-exercise surge - challenging assumptions that the quadriceps had been profoundly anaerobic while under load. On the contrary, it appears that aerobic metabolism contributes substantially, if not completely, to energy supply. A preliminary comparison of elite sailors with aerobic athletes suggests that isometric endurance at a given percentage MVC does not differ between the two groups, but the sailors have higher MVCs. In individuals not highly strength-trained, greater electromyogram activity immediately before capitulation than in an MVC performed while fresh indicates that physiological (not just volitional) limits have been reached. It is concluded that the literature and the outline of my recent work with colleagues support the view that the predominant physiological load during single-handed dinghy sailing is quasi-isometric in form and accounts for roughly half of the metabolic demand. Any more complete account of the physiology of hiking will require simultaneous on-water measurement of electromyographic, cardiovascular, and metabolic indicators in sailors extending from club to Gold Medal standard. 相似文献
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Three modern views about the factors limiting oxygen uptake in healthy humans are set against the original (early 1920s) concept of A. V. Hill and colleagues. The majority view for most of the intervening time has been that cardiac output is the essential limiting function. Among recent research in support of this contention is that, in quadrupeds, pericardiectomy, which allows greater diastolic filling, elevates maximum oxygen uptake; however, the relevance to bipedal exercise can be questioned. In any case, algebraic analyses of model systems indicate that all identifiable stages on the oxygen transport pathway, from pulmonary diffusion to oxidative phosphorylation in skeletal muscle mitochondria, materially influence maximum uptake. Thus, if a high cardiac output is to be of benefit, all the other steps must function better too. Nevertheless, these two viewpoints concur that the limit to maximum oxygen uptake is somatic. In contrast, there are strong indications that at altitudes where oxygen availability is about half that at sea level, cerebral oxygenation is a limiting factor, and some recent experiments raise the possibility that it might be a substantial influence at sea level also. Clearly, consensus cannot yet be reached on the question posed in the title. 相似文献
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