Heat acclimatization does not improve VO2max or cycling performance in a cool climate in trained cyclists

This study investigated if well-trained cyclists improve V ˙ O 2 m a x and performance in cool conditions following heat acclimatization through natural outdoor training in hot conditions. Eighteen trained male cyclists were tested for physiological adaptations, V ˙ O 2 m a x , peak aerobic power output, exercise efficiency, and outdoor time trial (TT) performance (43.4 km in cool environment, ∼5-13 °C) before and after 2 weeks of training in a cool (CON, n = 9) or hot (∼35 °C, HA, n = 9) environment. After heat acclimatization, TT performance in the heat was improved by 16%; however, there was no change in the HA group in V ˙ O 2 m a x (4.79 ± 0.21 L/min vs 4.82 ± 0.35 L/min), peak aerobic power output (417 ± 16 W vs 422 ± 17 W), and outdoor TT performance in cool conditions (300 ± 14 W/69 ± 3 min vs 302 ± 9 W/69 ± 4 min). The present study shows that 2 weeks of heat acclimatization was associated with marked improvements in TT performance in the heat. However, for the well-trained endurance athletes, this did not transfer to an improved aerobic exercise capacity or outdoor TT performance in cool conditions.

Time course of natural heat acclimatization in well-trained cyclists during a 2-week training camp in the heat

The aim of this study was to determine the time course of physiological adaptations and their relationship with performance improvements during 2 weeks of heat acclimatization. Nine trained cyclists completed 2 weeks of training in naturally hot environment (34 ± 3 °C; 18 ± 5% relative humidity). On days 1, 6, and 13, they performed standardized heat response tests (HRT-1, 2, 3), and 43.4-km time trials in the heat (TTH-1, 2, 3) were completed on days 2, 7, and 14. Within the first 5-6 days, sweat sodium concentration decreased from 75 ± 22 mmol/L to 52 ± 24 mmol/L, sweat rate increased (+20 ± 15%), and resting hematocrit decreased (-5.6 ± 5.4%), with no further changes during the remaining period. In contrast, power output during TTHs gradually improved from TTH-1 to TTH-2 (+11 ± 8%), and from TTH-2 to TTH-3 (+5 ± 4%). Individual improvements in performance from TTH-1 to TTH-2 correlated with individual changes in hematocrit (assessed after the corresponding HRT; r = -0.79, P < 0.05), however, were not related to changes in performance from TTH-2 to TTH-3. In trained athletes, sudomotor and hematological adaptations occurred within 5-6 days of training, whereas the additional improvement in performance after the entire acclimatization period did not relate to changes in these parameters.

Age-related changes in vertebral and iliac crest 3D bone microstructure--differences and similarities

Age-related changes of vertebra and iliac crest 3D microstructure were investigated, and we showed that they were in general similar. The 95th percentile of vertebral trabecular thickness distribution increased with age for women. Surprisingly, vertebral and iliac crest bone microstructure was only weakly correlated (r = 0.38 to 0.75), despite the overall similar age-related changes.

INTRODUCTION

The purposes of the study were to determine the age-related changes in iliac and vertebral bone microstructure for women and men over a large age range and to investigate the relationship between the bone microstructure at these skeletal sites.

METHODS

Matched sets of transiliac crest bone biopsies and lumbar vertebral body (L2) specimens from 41 women (19-96 years) and 39 men (23-95 years) were micro-computed tomography (μCT) scanned, and the 3D microstructure was quantified.

RESULTS

For both women and men, bone volume per total volume (BV/TV), connectivity density (CD), and trabecular number (Tb.N) decreased significantly, while structure model index (SMI) and trabecular separation (Tb.Sp) increased significantly with age at either skeletal site. Vertebral trabecular thickness (Tb.Th) was independent of age for both women and men, while iliac Tb.Th decreased significantly with age for men, but not for women. In general, the vertebral and iliac age-related changes were similar. The 95th percentile of the Tb.Th distribution increased significantly with age for women but was independent of age for men at the vertebral body, while it was independent of age for either sex at the iliac crest. The Tb.Th probability density functions at the two skeletal sites became significantly more similar with age for women, but not for men. The microstructural parameters at the iliac crest and the vertebral bodies were only moderately correlated from r = 0.38 for SMI in women to r = 0.75 for Tb.Sp in men.

CONCLUSION

Age-related changes in vertebral and iliac bone microstructure were in general similar. The iliac and vertebral Tb.Th distributions became more similar with age for women. Despite the overall similar age-related changes in trabecular bone microstructure, the vertebral and iliac bone microstructural measures were only weakly correlated (r = 0.38 to 0.75).

Understanding of basic mechanisms of beta-cell function and survival: prelude to new diabetes therapies

Type 1 and type 2 diabetes are both diseases of insulin insufficiency, although they develop by distinct pathways. The recent surge in the incidence of type 2 diabetes and the chronic ailments confronted by patients with either form of the disease highlight the need for better understanding of beta-cell biology. In this review, we present recent work focused on this goal. Our hope is that basic research being conducted in this and other laboratories will ultimately contribute to the development of methods for enhancing beta-cell function and survival in the context of both major forms of diabetes. Our strategy for understanding the beta-cell involves a multidisciplinary approach in which tools from the traditional fields of biochemistry, enzymology, and physiology are teamed with newer technologies from the fields of molecular biology, gene discovery, cell and developmental biology, and biophysical chemistry. We have focused on two important aspects of beta-cell biology in our studies: beta-cell function, specifically the metabolic regulatory mechanisms involved in glucose-stimulated insulin secretion, and beta-cell resistance to immune attack, with emphasis on resistance to inflammatory cytokines and reactive oxygen species.

Socioeconomic status, occupation, and risk of hospitalisation due to coxarthrosis in Denmark 1981-99

OBJECTIVES

To predict the relative risk and time trend in hospitalisation due to coxarthrosis (CA) among groups of different socioeconomic status and occupations in order to test existing aetiological hypotheses.

METHODS

Four consecutive cohorts of all gainfully employed Danish men were followed up for CA. Standardised hospitalisation ratios (SHR) and time trends were calculated.

RESULTS

Self employed men had an SHR due to CA of 140 (95% confidence interval (CI) 130 to 151) in 1994-99. It changed -1.2% (95% CI -2 to -0.4) annually from 1981 to 1999. Self employed farmers had an SHR of 286 (95% CI 262 to 313) during 1994-99, increasing 0.14% a year (95% CI -0.9 to 1.1) from 1981 to 1999. Unskilled men had an SHR of 121 (95% CI 113 to 130) in 1994-99. The SHR increased 1.6% annually (95% CI 0.7 to 2.4) from 1981 to 1999. Employed agricultural workers had an SHR of 189 (95% CI 158 to 227) from 1994 to 1999. The SHR increased 3.7% annually (95% CI 1.2 to 6.2) from 1981 to 1999.

CONCLUSIONS

The relative risk of hospitalisation due to CA was consistently high among farmers in four successive analyses spanning an 18 year period. The relative risks remained stable over time despite the fact that the number of farmers decreased. The risk increased among employed workers in agriculture and horticulture over that period, and an increased risk was also found among tractor drivers and a few other occupations.

Stimulus/secretion coupling factors in glucose-stimulated insulin secretion: insights gained from a multidisciplinary approach

There is a growing appreciation for the complexity of the pathways involved in glucose-stimulated insulin secretion (GSIS) from pancreatic islet beta-cells. In our laboratory, this has stimulated the development of an interdisciplinary approach to the problem. In this study, we review recent studies combining the tools of recombinant adenovirus for gene delivery, the development of novel cell lines that exhibit either robust or weak GSIS, and nuclear magnetic resonance imaging for metabolic fingerprinting of glucose-stimulated cells. Using these tools, we demonstrate a potentially important role for pyruvate carboxylase-mediated pyruvate cycling pathways in the control of GSIS, and discuss potential coupling factors produced by such pathways.

A futile metabolic cycle activated in adipocytes by antidiabetic agents

Thiazolidinediones (TZDs) are effective therapies for type 2 diabetes, which has reached epidemic proportions in industrialized societies. TZD treatment reduces circulating free fatty acids (FFAs), which oppose insulin actions in skeletal muscle and other insulin target tissues. Here we report that TZDs, acting as ligands for the nuclear receptor peroxisome proliferator-activated receptor (PPAR)-gamma, markedly induce adipocyte glycerol kinase (GyK) gene expression. This is surprising, as standard textbooks indicate that adipocytes lack GyK and thereby avoid futile cycles of triglyceride breakdown and resynthesis from glycerol and FFAs. By inducing GyK, TZDs markedly stimulate glycerol incorporation into triglyceride and reduce FFA secretion from adipocytes. The 'futile' fuel cycle resulting from expression of GyK in adipocytes is thus a novel mechanism contributing to reduced FFA levels and perhaps insulin sensitization by antidiabetic therapies.

[Workload, gender and age among personnel with reported sudden lifting injuries]

INTRODUCTION

In 1996 the Danish Parliament passed a new Act on industrial injuries, including the so-called sudden lifting injuries. This type of lifting injury had been experienced in some industries in connection with lifting situations causing sudden pain in the back. Less frequently, other regions of the body may be affected. This study is a distribution of a sample of reported industrial injuries of this type in groups according to types of lifts. The study also includes a comparison with parameters from the Danish Work Environment Cohort Study.

MATERIAL AND METHODS

The sample consisted of a total of 482 cases of back injuries. Of these, 346 cases were distributed according to six categories of manual lifting work and to age and gender. The rest, 136 cases, were excluded for technical reasons.

RESULTS

In the distribution, 8% of the cases were in jobs with many heavy lifts, 66% of the cases were in jobs with moderate daily lifted weights or in jobs with only few or light lifts. Approximately 25% of cases concerned employees performing patient transfers. The distribution contained more men than the Danish Work Environment Cohort Study, and the persons in the cases were slightly older than this reference population.

DISCUSSION

Altogether, this study points towards an occurrence of sudden lifting injuries among employees performing certain types of manual lifting work. The industrial injuries cases may have been subject to some selection.

Role of acyl-CoA binding protein in acyl-CoA metabolism and acyl-CoA-mediated cell signaling

Long-chain acyl-CoA esters (LCA) act both as substrates and intermediates in metabolism and as regulators of various intracellular functions. Acyl-CoA binding protein (ACBP) binds LCA with high affinity and is believed to play an important role in intracellular acyl-CoA transport and pool formation and therefore also for the function of LCA as metabolites and regulators of cellular functions . The free concentration of cytosolic LCA is efficiently buffered to low nanomole concentration by ACBP and fatty acid binding protein (FABP). An additional important factor is the activity of acyl-CoA hydrolases. The estimated cellular free LCA concentration is two to four orders of magnitude lower than the concentrations reported to be necessary to regulate most LCA-affected cellular functions. Preliminary evidence indicates that the regulatory effect of LCA might be mediated by the LCA/ACBP complex.

Role of acylCoA binding protein in acylCoA transport, metabolism and cell signaling

Long chain acylCoA esters (LCAs) act both as substrates and intermediates in intermediary metabolism and as regulators in various intracellular functions. AcylCoA binding protein (ACBP) binds LCAs with high affinity and is believed to play an important role in intracellular acylCoA transport and pool formation and therefore also for the function of LCAs as metabolites and regulators of cellular functions [1]. The major factors controlling the free concentration of cytosol long chain acylCoA ester (LCA) include ACBP [2], sterol carrier protein 2 (SCP2) [3] and fatty acid binding protein (FABP) [4]. Additional factors affecting the concentration of free LCA include feed back inhibition of the acylCoA synthetase [5], binding to acylCoA receptors (LCA-regulated molecules and enzymes), binding to membranes and the activity of acylCoA hydrolases [6].

[Prolapsed cervical intervertebral disk in professional drivers in Denmark 1981-1990]

The aim of this study was to estimate the risk of being hospitalized due to prolapsed cervical interverteral disc among male professional drivers in Denmark. A cohort consisting of all economically active persons in Denmark, identified January 1981, gives information on the most important occupation during 1980. The cohort was followed for ten years. Additional data on occupational exposures were extracted from a national survey. Occupational groups such as bus and taxi-cab drivers were found to have an increased risk, of cervical prolapse as did the group of professional drivers as a whole.

Incidence of lung cancer among cobalt-exposed women

OBJECTIVES

The purpose of this study was to estimate the risk of lung cancer for women occupationally exposed to cobalt-aluminate spinel.

METHODS

A retrospective cohort of 874 women occupationally exposed to cobalt in two Danish porcelain factories and 520 women not exposed to cobalt were identified from personnel files. Vital status was assessed in the national population register, and incident cancer cases were traced in the national cancer register. Thirteen women (0.92%) were lost to follow-up. The observed deaths and incident cancer cases were compared with the expected number based on rates for all Danish women.

RESULTS

The total mortality of the cohort was the same as for all Danish women. The incidence of all cancer was slightly elevated among the exposed women (67 observed, 55.8 expected) and equal to the expected in the reference group (60 observed, 60.6 expected). An increased lung cancer incidence was found both in the exposed group [8 cases, standardized incidence rate (SIR) 2.35, 95% confidence interval (95% CI) 1.01-4.6] and in the reference group (7 cases, SIR 1.99, 95% CI 0.8-4.1). The exposed group had a relative risk ratio of 1.2 (95% CI 0.4-3.8) when compared with the reference group.

CONCLUSIONS

Both the cobalt-exposed group and the reference group had an increased lung cancer risk compared with all Danish women, but the risk was only slightly higher for the exposed group than for the reference group. The study was based on few persons, and we recommend a follow-up after five years.

Prolapsed cervical intervertebral disc in male professional drivers in Denmark, 1981-1990. A longitudinal study of hospitalizations

STUDY DESIGN

This study of professional drivers is a part of a longitudinal record linkage study of all economically active men in Denmark, identified on January 1, 1981. Information about the main occupation was identified in 1980. The cohort was followed for first hospitalization with prolapsed cervical intervertebral disc until December 31, 1990.

OBJECTIVES

To examine the risk of prolapsed cervical intervertebral disc in all Danish professional drivers, and to analyze exposures of the male drivers in a sample of all Danish male drivers.

SUMMARY OF BACKGROUND DATA

Only a few studies on occupation and prolapsed cervical intervertebral disc have been published. These studies suggest that professional driving may be a risk factor for development of prolapsed cervical intervertebral disc. Drivers are exposed to whole-body vibrations, heavy lifting, and a sedentary position. Other potential exposures are accelerations and decelerations and whiplash accidents. Such exposure may be involved in the causation of prolapsed cervical intervertebral disc.

METHODS

A standardized hospitalization ratio was calculated for each subgroup of drivers using all economically active people as the standard. Additional exposure information was extracted from a national survey on work environment.

RESULTS

Almost all men in occupations involving professional driving had a statistically significant elevated risk of being hospitalized with prolapsed cervical intervertebral disc.

CONCLUSIONS

Professional driving is a risk factor for prolapsed cervical intervertebral disc.

[Validity of the diagnosis "essential hypertension" in the National Patient Registry]

This study validated hypertension (ICD-8: 401.99) in The National Inpatient Register with reference to the use of the diagnosis in the Occupational Hospitalization Register. A university hospital and a regional hospital were chosen for the evaluation. A sample of case records with the discharge diagnosis essential hypertension and additional case records with other diagnoses were re-coded blindly and independently by two doctors. Cause of admission or admission diagnosis was recorded for essential hypertension cases. The agreement with The National Inpatient Register ranged from 60 to 40%. About half of the cases with the discharge diagnosis "essential hypertension" were admitted to hospital due to hypertension, about a quarter due to diagnoses within "other arteriosclerotic diseases" (ICD-8: 400, 402-440). The misclassification may lead to an underestimation of risks of hypertension in various occupations in the Occupational Hospitalization Register or bias the occupational risk pattern of essential hypertension to become more alike that of arteriosclerotic diseases.

[Occupation and lumbar disk prolapse]

All Danish occupational groups were screened for an increased risk of hospitalization due to a prolapsed lumbar intervertebral disc (PLID) (ICD-8: 725.11). A cohort of all gainfully employed Danes aged 20 to 59 years in 1981 was followed-up for 10 years for first hospitalization with PLID. A Standardized Hospitalization Ratio was calculated using all economically active persons as the reference group. Male groups with an elevated risk were found in building and construction, the iron and metal industry, in the food and nutrition sector and in occupational driving. Almost all groups of professional drivers had an elevated risk. Female groups with an elevated risk were mainly found in the same industries, but home helps, service workers in the private sector and sewing machine operators also had an elevated risk. We conclude that there are significant and systematic differences between occupational groups as concerns the risk of hospital admission due to PLID.