Challenging a dogma of exercise physiology: does an incremental exercise test for valid VO 2 max determination really need to last between 8 and 12 minutes?

A widely cited recommendation is that to elicit valid maximal oxygen uptake (VO(2 max)) values, incremental exercise tests should last between 8 and 12 minutes. However, this recommendation originated from the findings of a single experimental study conducted by Buchfuhrer et al. in 1983. Although this study is an important contribution to scientific knowledge, it should not be viewed as sufficient evidence to support the recommendation for eliciting valid VO(2 max) values. At least eight studies have reported that durations as short as 5 minutes and as long as 26 minutes elicit VO(2 max) values similar to those derived from tests of 8-12 minutes' duration. Two studies reported that the shorter test protocols elicited significantly higher VO(2 max) values in untrained men and women. In three studies that reported significantly higher VO(2 max) values determined during tests of 8-12 minutes than during more prolonged tests, the prolonged tests were associated with maximal treadmill grades of 20-25%, compared with 6-10% in the shorter tests. Therefore, intolerable treadmill grades, rather than the prolonged test duration, may have limited the ability to elicit VO(2 max). In view of the available evidence, test administrators, reviewers and journal editors should not view 8-12 minutes' duration for incremental exercise tests as obligatory for valid VO(2 max) determination. Current evidence suggests that to elicit valid VO(2 max) values, cycle ergometer tests should last between 7 and 26 minutes and treadmill tests between 5 and 26 minutes. This is dependent on the qualification that short tests are preceded by an adequate warm-up and that treadmill grades do not exceed 15%. Current research is too limited to indicate appropriate test duration ranges for discontinuous test protocols, or protocols incorporating high treadmill grades.     

What governs skeletal muscle VO2max? New evidence

Recent investigations into the determinants of skeletal muscle maximal oxygen consumption (VO2) have provided further evidence regarding the role of O2 supply and demand in governing exercise metabolism. Specifically, four studies utilizing both animal and human exercise models are highlighted here: 1) the role of the diffusive O2 component was examined in the exercising canine gastrocnemius muscle by a rightward shift in the O2 dissociation curve while maintaining O2 delivery constant; 2) the role of peripheral and central components was examined by studying the human quadriceps muscle, already recognized to have a very high mass specific O2 delivery, under conditions of increased (hyperoxia) and reduced O2 availability (hypoxia); 3) the role of intracellular PO2 in the progressive increase in lactate efflux from skeletal muscle from submaximal to maximal effort; and finally 4) the role of intracellular PO2 itself as a determinant of maximal mitochondrial O2 consumption. In summary, these investigations illustrate 1) the importance of the diffusion gradient from blood to muscle cell; 2) illustrate that even in functionally isolated trained skeletal muscle the highest recorded metabolic rates can be increased by increasing O2 supply; 3) that a constant intracellular PO2 during graded exercise is therefore unrelated to increasing lactate efflux; and 4) that only in hyperoxia does trained human skeletal muscle approaching very high mitochondrial metabolic limits, as shown by a disproportionate increase in intracellular PO2 for the recorded change in VO2max.     

Time at VO2max during intermittent treadmill running: test protocol dependent or methodological artefact?

Effects of methodological differences on the determination of time at VO (2max) (t (VO2max)) during intermittent treadmill running were investigated. Subjects performed three incremental tests to volitional exhaustion: a continuous protocol with 1-min stages (Cont-INC ([1-min])), and two discontinuous protocols of 2-min (Dis-INC ([2-min])) and 3-min (Dis-INC ([3-min])) stage durations. For each test, VO (2max) and the running velocity associated with V.O (2max) (vVO (2max)) were determined. On a fourth visit, subjects performed an intermittent test with 30-s work and relief intervals run at 105 % and 60 %, respectively, of the vV. (2max) determined during Cont-INC ((1-min)). The t (VO2max) during the intermittent test was determined using three different criteria: VO (2) data points > or = 100 % VO (2max) determined in Cont-INC ((1-min)) (t (VO2max[100 %])), > or = 95 % VO (2max) (t (VO2max[95 %])) and > or = VO (2max) minus 2.1 ml . kg (-1) . min (-1) (t (VO2max[- 2.1])). The V.O (2max) means (SD) for Cont-INC ((1-min)), Dis-INC ((2-min)) and Dis-INC ((3-min)) were 4093 (538), 4096 (516), and 3980 (488) mL . min (-1), respectively. The t (VO2max) means (SD) were: t (VO2max(100 %)) 163 (227) s, t (VO2max(95 %)) 418 (439) s, and t (VO2max(- 2.1)) 358 (395) s. All differences in t (V.O2max) were significantly different (p < 0.05). Differences in t (VO2max) due to using V.O (2max) values derived from using different V.O (2) time-averages were significantly different (p < 0.05). Methodological differences should be considered during interpretation of previous studies.     

Is exercise effective treatment for osteoarthritis of the knee?

OBJECTIVE: To review and determine the effectiveness of exercise treatment in osteoarthritis of the knee. METHODS: A computerised literature search of Medline was carried out searching between June 1966 and January 2000. RESULTS: Twenty three randomised controlled trials were identified from the literature. Only three trials were sufficiently powered. Small to moderate beneficial effects of exercise treatment were found for pain, small beneficial effects on disability outcome measures, and moderate to great beneficial effects were observed according to patient global assessment of effect. It was not possible to obtain evidence on the content of exercise interventions, as studies were hampered by lack of attention to proper concealment, reporting of adverse effects, and long term effects of exercise treatment. The lack of standard outcomes measures is also noted. CONCLUSIONS: The available evidence indicates beneficial short term effects of exercise treatment in patients with osteoarthritis of the knee. However, the number of available studies is limited, and more research is needed to expand this recommendation. Specifically, additional trials should provide information on adherence, home based interventions, interaction with pharmacological treatments, functional outcomes measures relevant to exercise treatment in these patients, and long term effects. At present, doctors should recommend exercise to all patients with mild/moderate disease. Further study should be encouraged and exercise should be continued to be recommended as a mainstay of non-pharmacological treatment of osteoarthritis of the knee.     

外呼吸功能对VO2max影响的初步探讨

１２名优秀中长跑运动员在跑台上进行递增负荷的运动过程中测定气体代谢各指标。结果表明：肺活量与ＶＯ２ｍａｘ呈正相关，ｒ＝０．７９９，Ｐ＜０．０１。在测定ＶＯ２ｍａｘ的运动过程中，呼吸频率与ＴＲＵＥＯ_２随强度的增加而递增，两者呈正相关，其相关系数分别在０．４６８－０．７８７之间，Ｐ＜０．０１，但在呼吸频率达到４４次／分后呼吸频率继续增长，而ＴＲＵＥＯ_２逐渐下降，呈负相关，ｒ＝－０．４２６至－０．９０７之间，Ｐ＜０．０１，ＴＲＵＥＯ_２的下降，反映了肺通气效率的下降，肺活量、呼吸频率的调节和ＴＲＵＥＯ_２的变化与ＶＯ２ｍａｘ的水平有着内在的联系。     

Is exercise of value in the prevention of fragility fractures in men?

Exercise during growth seems to build a stronger skeleton resulting in a high peak bone mineral density (BMD) in men. Exercise during adulthood produces benefits in BMD or prevents bone loss, but the changes are of minor biological significance as regards fracture reduction. However, prospective intervention studies suggest exercise to improve muscle strength, co-ordination and balance, even in octogenarians—all traits possible to reduce the number of falls. It is virtually impossible to undertake a randomized blinded study of exercise with fracture as end point due to the large cohorts needed. Retrospective and prospective observational and case control studies suggest activity to be associated with reduced fracture risk. This may be correct, but consistently replicated sampling bias may produce the same observation. The Achilles heel of exercise is the cessation of physical activity. Biologically important benefits in BMD or improvement in muscle size and strength achieved by exercise during growth and young adulthood seem to be eroded in retirement, leaving virtually no remaining benefits in old age, the period when fragility fractures exponentially rise. On the contrary, continued exercise on a lower level may maintain some of the musculoskeletal benefit, but dose– response relationships need to quantified, as do the effects of exercise on bone size, shape, architecture and frequency of injurious falls. Absence of evidence is not evidence of absence of effect, but if we recommend exercise then should this be to children, adults, elderly men or men with fractures? What type of exercise? For how long? How many fewer fractures will result in the community from a community based exercise campaign like the anti-tobacco campaign? The higher level of proof, suggesting exercise to reduce spine and hip fractures must come from well designed and executed prospective randomized studies. Blinded studies obviously cannot be done but open trials can, and should be undertaken.     

Is pneumatization of middle turbinates compensatory or congenital?

Objective

To determine the frequency of concha bullosa (CB) and the association between the degree of pneumatization and the severity of septum deviation in both paediatric and adult groups by CT evaluation and to investigate whether the pneumatization of middle turbinates is compensatory or congenital.

Method

We retrospectively reviewed digitally stored paranasal sinus CT images of 86 paediatric and 204 adult patients. The severity of the deviation and cross-sectional area of the pneumatized area of the CB were determined using tomography images. The septums were divided into three groups according to the severity of deviation. The cross-sectional area of the contralateral side divided by the cross-sectional area of the deviation was calculated and described as the interturbinate ratio.

Results

When bilateral CB was found, the pneumatization of the CB was more prominent on the contralateral side than on the deviation side in both the paediatric and the adult groups. However, we found that the interturbinate ratios were not statistically different between the paediatric and adult groups. Also, the interturbinate ratios were independent degrees of deviation in children and adults. The frequency of CB was low in the adult group compared with the paediatric group.

Conclusion

Interturbinate ratios were not statistically different between paediatric and adult groups and were independent of the severity of deviation. These findings suggest that the pneumatization process is not compensatory.     

Is there a role for exercise in the prevention of osteoporotic fractures?

OBJECTIVES: To examine whether there is a role for exercise in improving bone mineral density (BMD), particularly in postmenopausal women. The effects of different types of exercise are examined together with their effects at selected skeletal sites. The role of activity in reducing falls and hip fractures will also be considered as well as the potentially negative effects of excessive exercise. METHODS: A literature search over the past 20 years was conducted and landmark papers selected. RESULTS: Certain types of exercise have been found to exert moderate benefits on BMD of the wrist, spine, and hip. Most studies do not detect a difference between the effects of endurance activities and strength training for BMD of the spine. It has been more difficult to isolate the optimal type of activity for effecting an osteogenic response at the hip, but recent evidence suggests that high impact work such as stepping and jumping may be effective at this site. The combination of hormone replacement therapy and exercise would appear to be more effective than either intervention on its own. Certain types of exercises have additional benefits, such as muscle strengthening, which could reduce the incidence of falls. Excessive exercise can lead to menstrual disturbances in female athletes and this in turn can cause bone loss, particularly from the spine. CONCLUSIONS: Exercise across the life span should be encouraged in order to maximise peak bone mass, reduce age related bone loss, and maintain muscle strength and balance. Although the effects of exercise on BMD later in life are small, epidemiological evidence suggests that being active can nearly halve the incidence of hip fractures in the older population. This effect is most probably multifactorial through the positive effects on bone, muscle strength, balance, and joint flexibility. Younger women should be aware of the dangers to the skeleton of menstrual disorders.     

VO(2) slow component: to model or not to model?

PURPOSE: The purpose of this study was to compare several techniques often used in the literature for measuring the amplitude of the slow component of oxygen uptake kinetics. METHODS: Eight healthy male volunteer cyclists performed two identical bouts of square wave cycle ergometry, from a VO(2) of 60% of the lactic acid threshold (LAT) to 30% of the difference between LAT and VO(2) peak. Predetermined intervals (3--6 and 3--10 min) were chosen to reflect those often used in the literature, namely 3-6 min and 3 min to the end of exercise. Several procedures were used to estimate the 3, 6, and 10-min VO(2) values (20-s averaging, 60-s averaging, and mono-exponential modeling). These were compared with the modeled slow component amplitude using a two-phase model with independent time delays: VO(2)(t) = B VO(2) + A(1)(1 -- e(-(t-TD1)/tau(1)) + A(2)(1 -- e(-(t-TD2)/tau(2)). CONCLUSIONS: The results showed a significant underestimation for all methods of slow component amplitude estimation (P < 0.05) when compared with the actual (modeled) amplitude. In so far as research on oxygen uptake kinetics is used to understand the underlying physiology, it is imperative that the components of the kinetics be determined accurately. The use of a predetermined time frame for estimation of the amplitude of the slow component is not supported by this study. Future investigations should consider these results and make every effort to model the underlying response.     

Is there an association between physical exercise and the quality of life of hypertensive patients?

CONTEXT: Quality of life of hypertensive patients (QOLHP) is associated with factors that are not always taken into account in the recommendations made by doctors. OBJECTIVE: To evaluate the association between QOLHP and physical exercise in an effectiveness approach, i.e. under the actual conditions of application of these treatments. METHODOLOGY: In a sample of 361 hypertensive patients registered in a primary care center in Tenerife, Spain, the QOLHP is measured using the PECVEC questionnaire. The main factor considered is physical exercise. In addition, we compiled a set of control variables: pharmacological and dietetic treatments, pathological, clinical, functional, psychological, social, lifestyle and demographic characteristic of the patients. We explored the association between all these factors and the QOLHP by adjusting multiple linear regression models. RESULTS: The PECVEC results were between 2.0 and 3.5, with an overall Cronbach's alpha reliability statistic of 0.88. From the sample, 58% of the patients engage in physical exercise, 75% maintain a anti-hypertension diet and 89% take hypertension medication. From all the treatments evaluated, only physical exercise is associated directly with all PECVEC scales, especially for women and patients over 65. CONCLUSIONS: Recommending the practice of physical exercise may be a useful tool for doctors to improve the QOLHP.     

Is lactic acidosis a cause of exercise induced hyperventilation at the respiratory compensation point?

Objectives: The respiratory compensation point (RCP) marks the onset of hyperventilation ("respiratory compensation") during incremental exercise. Its physiological meaning has not yet been definitely determined, but the most common explanation is a failure of the body's buffering mechanisms which leads to metabolic (lactic) acidosis. It was intended to test this experimentally.

Methods: During a first ramp-like exercise test on a cycle ergometer, RCP (range: 2.51–3.73 l*min^–1 oxygen uptake) was determined from gas exchange measurements in five healthy subjects (age 26–42; body mass index (BMI) 20.7–23.9 kg*m^–2; VO_2peak 51.3–62.1 ml*min^–1*kg^–1). On the basis of simultaneous determinations of blood pH and base excess, the necessary amount of bicarbonate to completely buffer the metabolic acidosis was calculated. This quantity was administered intravenously in small doses during a second, otherwise identical, exercise test.

Results: In each subject sufficient compensation for the acidosis, that is, a pH value constantly above 7.37, was attained during the second test. A delay but no disappearance of the hyperventilation was present in all participants when compared with the first test. RCP occurred on average at a significantly (p = 0.043) higher oxygen uptake (+0.15 l*min^–1) compared with the first test.

Conclusions: For the first time it was directly demonstrated that exercise induced lactic acidosis is causally involved in the hyperventilation which starts at RCP. However, it does not represent the only additional stimulus of ventilation during intense exercise. Muscle afferents and other sensory inputs from exercising muscles are alternative triggering mechanisms.

     

Antioxidant supplementation during exercise training: beneficial or detrimental?

High levels of reactive oxygen species (ROS) produced in skeletal muscle during exercise have been associated with muscle damage and impaired muscle function. Supporting endogenous defence systems with additional oral doses of antioxidants has received much attention as a noninvasive strategy to prevent or reduce oxidative stress, decrease muscle damage and improve exercise performance. Over 150 articles have been published on this topic, with almost all of these being small-scale, low-quality studies. The consistent finding is that antioxidant supplementation attenuates exercise-induced oxidative stress. However, any physiological implications of this have yet to be consistently demonstrated, with most studies reporting no effects on exercise-induced muscle damage and performance. Moreover, a growing body of evidence indicates detrimental effects of antioxidant supplementation on the health and performance benefits of exercise training. Indeed, although ROS are associated with harmful biological events, they are also essential to the development and optimal function of every cell. The aim of this review is to present and discuss 23 studies that have shown that antioxidant supplementation interferes with exercise training-induced adaptations. The main findings of these studies are that, in certain situations, loading the cell with high doses of antioxidants leads to a blunting of the positive effects of exercise training and interferes with important ROS-mediated physiological processes, such as vasodilation and insulin signalling. More research is needed to produce evidence-based guidelines regarding the use of antioxidant supplementation during exercise training. We recommend that an adequate intake of vitamins and minerals through a varied and balanced diet remains the best approach to maintain the optimal antioxidant status in exercising individuals.