Vastus Lateralis Motor Unit Recruitment Thresholds Are Compressed towards Lower Forces in Older Men.

BACKGROUND: Aging results in adaptations which may affect the control of motor units. OBJECTIVE: We sought to determine if younger and older men recruit motor units at similar force levels. DESIGN: Cross-sectional, between-subjects design. SETTING: Controlled laboratory setting. PARTICIPANTS: Twelve younger (age = 25 ± 3 years) and twelve older (age = 75 ± 8 years) men. MEASUREMENTS: Participants performed isometric contractions of the dominant knee extensors at a force level corresponding to 50% maximal voluntary contraction (MVC). Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis. A surface EMG signal decomposition algorithm was used to quantify the recruitment threshold of each motor unit, which was defined as the force level corresponding to the first firing. Recruitment thresholds were expressed in both relative (% MVC) and absolute (N) terms. To further understand age-related differences in motor unit control, we examined the mean firing rate versus recruitment threshold relationship at steady force. RESULTS: MVC force was greater in younger men (p = 0.010, d = 1.15). Older men had lower median recruitment thresholds in both absolute (p = 0.005, d = 1.29) and relative (p = 0.001, d = 1.53) terms. The absolute recruitment threshold range was larger for younger men (p = 0.020; d = 1.02), though a smaller difference was noted in relative terms (p = 0.235, d = 0.50). These findings were complimented by a generally flatter slope (p = 0.070; d = 0.78) and lower y-intercept (p = 0.009; d = 1.17) of the mean firing rate versus recruitment threshold relationship in older men. CONCLUSION: Older men tend to recruit more motor units at lower force levels. We speculate that recruitment threshold compression may be a neural adaptation serving to compensate for lower motor unit firing rates and/or denervation and subsequent re-innervation in aged muscle.

Increasing incidence of cutaneous melanoma in Queensland, Australia.

BACKGROUND: Queensland, Australia, had the world's highest incidence rates of invasive cutaneous melanoma in the 1970s. PURPOSE: The purpose of this study was to monitor trends in melanoma incidence in Queensland. METHODS: We studied two time periods in which ascertainment was comparable. RESULTS: In the 7.5 years up to 1987, the incidence of invasive melanoma in Queensland increased by more than one half in women (to 42.89 per 100,000) and more than doubled in men (to 55.81 per 100,000), with the most dramatic increase seen in men over age 50 years. This higher increase in men is a reversal of the previously higher rates in women. In Queensland, cumulative risks of total cutaneous melanoma (in persons aged 0-74 years), including preinvasive melanoma, have increased to one in 14 in men and to one in 17 in women. There were large increases in age-standardized incidence rates of thin lesions (less than 0.75 mm) in both sexes but not of in situ lesions, and there were also increases in thicker lesions, especially on the backs of males. CONCLUSIONS: Although increased awareness and earlier diagnosis appear to have accompanied increased incidence, increased exposure to solar UV radiation during the past 50 years appears to be the most likely explanation for the rise in incidence rates. IMPLICATIONS: A better understanding is needed of the causes of melanoma and of the complex relationships between constitutional factors, ambient UV radiation, and sun-exposure behavior.

Nutrients in diet and plasma and risk of in situ cervical cancer.

Both plasma and dietary measures of vitamin A status were investigated along with previously established risk factors (number of sexual partners, age at first intercourse, smoking, and oral contraceptive use) in a study of 117 in situ cervical cancer patients and 196 matched community controls in Sydney, Australia. Neither total calories nor retinol from foods was related to cancer risk, nor was plasma retinol. When plasma and dietary indexes were considered together, vitamin C, fruit juices, and plasma beta-carotene showed protective effects. Plasma beta-carotene reduced risk from top to bottom quartile by 80%, vitamin C by 60%, and fruit juices by 50%. Thus the evidence suggests that cancer risk is associated with some aspect of diet that is reflected in the effect of plasma beta-carotene. There is no clear effect of any one nutrient but fruit juices appear protective. Thus vitamin C and beta-carotene are likely candidates.

Randomized trial of intake of fat, fiber, and beta carotene to prevent colorectal adenomas.

BACKGROUND: Epidemiologic evidence of associations between the high intake of fat and low intake of dietary fiber, beta carotene, and other dietary constituents and the risk of colorectal neoplasia has been inconsistent and has not provided a sufficient basis for recommendations concerning the dietary prevention of large-bowel cancer in humans. PURPOSE: We conducted a clinical trial to assess the effects on the incidence of adenomas of reducing dietary fat to 25% of total calories and supplementing the diet with 25 g of wheat bran daily and a capsule of beta carotene (20 mg daily). METHODS: We performed a randomized, partially double-blinded, placebo-controlled factorial trial in which half the patients were assigned to each intervention, resulting in seven intervention groups and one control group. Eligibility criteria included histologic confirmation of at least one colorectal adenoma and confidence expressed by the colonoscopist that all polyps had been removed. Dietary changes were individually initiated and monitored by dietitians and research nurses. At surveillance colonoscopy, the size and location of all polyps were recorded, and their histology was later centrally reviewed. Among 424 patients who were randomly assigned in the trial, 13 were found to be ineligible upon histologic review. Among the remaining 411, complete outcome data were collected from 390 at 24 months and from 306 at 48 months. All P values are from two-sided tests of statistical significance. RESULTS: There was no statistically significant prevention of total new adenomas with any of the interventions. We found a statistically non-significant reduced risk of large adenomas (> or = 10 mm) with the low-fat intervention: At 24 months, the odds ratio (OR) adjusted for potential confounders = 0.4 and 95% confidence interval (CI) = 0.1-1.1; at 48 months, OR = 0.3 and 95% CI = 0.1-1.0. Less and statistically nonsignificant reductions in the risk of large adenomas were found with wheat bran: At 24 months, OR = 0.8 and 95% CI = 0.3-2.2; at 48 months, OR = 0.8 and 95% CI = 0.3-2.5. Patients on the combined intervention of low fat and added wheat bran had zero large adenomas at both 24 and 48 months, a statistically significant finding (P = .03). CONCLUSIONS: Because only small numbers of patients were studied, our finding that the combination of fat reduction and a supplement of wheat bran reduced the incidence of large adenomas in this randomized, controlled trial must be treated with caution. The results do suggest, however, that these interventions may reduce the transition from smaller to larger adenomas, a step that may critically define those adenomas most likely to progress to malignancy.

Smoking and infectious agents and risk of in situ cervical cancer in Sydney, Australia.

In a study of 116 in situ cervical cancer patients and 193 matched community controls in Sydney, Australia, smoking was found to be a major risk factor. Current smokers had a adjusted relative risk [RR] of 4.5 compared to nonsmokers [95% confidence interval (CI) 2.2-9.1] and exsmokers a RR of 1.3 [95% CI 0.6-3.0]. There was a stepwise dose-response relationship between risk and number of cigarettes smoked (30+ cigarettes/day, RR = 5.1, 95% CI 1.5-17.3); this dose-response relationship was more marked among current smokers. Years of cigarette smoking was not consistently related to risk. Exposures to herpes simplex virus type 2 and cytomegalovirus as measured by antibody prevalence were unrelated to risk (RR = 1.1 for both measures). However, cases appeared to have more exposure than controls to herpes simplex virus type 1 (RR = 2.3, 95% CI 1.1-4.4).

Diet, transit time, stool weight, and colon cancer in two Scandinavian populations.

In samples of adult men from two Scandinavian populations with 4-fold differences in colon cancer incidence, a comparison was made of estimated food records over 4 days, defecation habits, mouth-to-anus transit time, and stool weight. The "high incidence" group consumed more white wheat breads and total meat and beer, but less potatoes and milk than the "low incidence" group. Defecation habits were similar. Transit time and stool weight had few significant correlations with diet and defecation habits, but stool weights were higher in the low incidence group. The results are consistent with a possible protective role of dietary fiber, unrelated to transit time.

Changes in serum carotenoids in subjects with colorectal adenomas after 24 mo of beta-carotene supplementation. Australian Polyp Prevention Project Investigators.

The effect of beta-carotene supplementation on major serum carotenoid fractions (lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, and beta-carotene) was investigated in 224 people with colorectal adenomas (139 men, 85 women) recruited for the Australian Polyp Prevention Project (APPP). Each subject was randomly assigned to take either 20 mg beta-carotene/d or placebo over 24 mo. Besides the expected increase in serum concentration of beta-carotene (1073% in men, 839% in women), lycopene (176% in men) and alpha-carotene (211% in men and 166% in women) concentrations were also increased after body mass index, baseline concentration, change in respective carotenoid intake, and other confounding factors were adjusted for. The increase in serum concentrations of these carotenoids after beta-carotene supplementation suggests that beta-carotene may interact biologically with other carotenoids and such interaction would need to be taken into consideration when the protective effect of beta-carotene supplementation for cancer or other diseases is examined.

Mortality of Chinese in New South Wales, 1969-1978.

A high proportion of adult Chinese living in New South Wales were born elsewhere, most commonly in China. Mortality among these males from 1969-78 was due mainly to ischaemic heart disease (IHD) cancer and cerbrovascular disease. Females showed a similar general pattern. Chinese males had double the risk of dying from cerebrovascular death, but death rates from IHD were similar to those of the Australian population, although the risk of IHD was significantly lower in Chinese females. Male Chinese had significantly higher rates for cancers of the nasopharynx, lung, intestines and rectum, and stomach and liver, whereas females had a significantly higher risk for cancers of the lung and stomach. Mortality patterns were similar to those for United States Chinese. Apart from cancer, relatively little is known about the causes of death in China. Crude death rates only are available for very broad categories of causes of death. Most of our information on Chinese general mortality comes from studies of migrants, or their descendants overseas, mainly in South-East Asia and the USA. In the latter more detailed studies have been made of cancer mortality and cancer incidence than of other causes. The purpose of our study was to describe mortality in Chinese, born in China, and dying in the state of New South Wales from 1969-78.

Body-site distribution of melanocytic nevi in young Australian children.

OBJECTIVE: To investigate the body-site distribution of melanocytic nevi (MN) with respect to habitually and intermittently sun-exposed surfaces. DESIGN: Cross-sectional survey of MN prevalence. SETTING: Townsville (19.16 degrees S), Queensland, Australia. PARTICIPANTS: Random sample of 506 1- to 6-year-old white children who were born and raised in Townsville (response, 87.6%). MAIN OUTCOME MEASURES: Site-specific counts and densities (number per square meter) of MN. RESULTS: Densities of MN of all sizes were highest on the outer forearms, followed by the outer upper arms, neck, and face. The feet had the lowest density of MN. Densities of MN of 2 mm or greater were highest on the upper arms and trunk. Boys had higher densities of MN of all sizes on the neck than girls (P = .002). Girls had higher densities of MN of 2 mm or greater on the lower legs (P = .006) and thighs (P = .005) than boys. Habitually sun-exposed body sites had higher densities, particularly of small MN, than relatively sun-protected sites, and larger MN were most prevalent on the intermittently exposed skin of the trunk. CONCLUSIONS: These children have higher total body and site-specific MN counts and densities than children from elsewhere, and their MN are distributed over the body in a way that implicates exposure to sunlight. As sun exposure in childhood and MN are risk factors for melanoma, intervention studies are required to determine if MN can be prevented.

Solar UVR exposures of primary school children at three locations in Queensland.

The ultraviolet radiation (UVR) exposures of primary school children in Brisbane, Toowoomba and Mackay (latitudes 27 degrees 30', 27 degrees 33' and 21 degrees 15' south, respectively) were assessed over a period of 2 weeks at each location using UVR-sensitive polysulfone (PS) film badges attached at the shoulder. The students filled in questionnaires on their time spent outdoors for each day of the study. These data in conjunction with the ambient UVR measured by a detector/datalogger unit at each site were used to correlate the calculated exposures with those measured using the PS badges. Overall, the questionnaires indicated that the males spent more time outdoors and had higher measured UVR exposures than females. For both boys and girls at each location, there was a strong correlation between the mean measured UVR exposure and the ambient solar UVR at that location.

Accuracy of case-reported family history of melanoma in Queensland, Australia.

A positive family history is used in clinical practice as an indication of increased melanoma risk, yet there are no data on the accuracy of reported family histories of melanoma. The validity of case-reported family history of melanoma was assessed in the course of a family and twin study of melanoma in Queensland, Australia, conducted among the families of 2,118 melanoma cases diagnosed in Queensland between 1982 and 1990. A total of 913 melanoma cases made 1,267 reports of melanoma among their first-degree relatives. A total of 1,040 of these reports were checked, first through relatives themselves and then, if the relative also said they had had melanoma, through the relative's medical records. Medical confirmation of melanoma as the diagnosis was obtained for 623 reports (59.9%; 95% confidence interval 56.9-62.9): a false-positive reporting rate by cases of 40.1%. The level of false-positive reporting was lower for cases under 70 years of age, for women, for cases whose own diagnosis of melanoma was more than 5 years earlier, and for cases with three or more relatives with melanoma. Media campaigns in Queensland aimed at increasing skin cancer awareness, and confusion between melanoma and other more common actinic neoplasma (basal and squamous cell carcinomas), may partly explain the high false-positive reporting rate observed here. For this reason, It is difficult to generalize these findings to northern hemisphere populations where skin cancer is not such an important public health issue.

The Queensland Familial Melanoma Project: study design and characteristics of participants.

Family history of melanoma is associated with an increased risk for the disease. Neither the relative contributions of genetic and shared environmental factors to familial risk nor how genetic susceptibility is mediated are known. The Queensland Familial Melanoma Project was undertaken to investigate (a) the role of genetic susceptibility as indicated by skin type, pigmentation and the prevalence of naevi and (b) exposure to solar ultraviolet radiation, and their interaction in the aetiology of familial melanoma. After obtaining doctor's consent, a brief family history questionnaire was mailed to all Queensland residents with a first primary cutaneous melanoma diagnosed between 1982 and 1990. Detailed information on melanoma history and standard melanoma risk factors was sought from all responding twins and familial cases, from a sample of non-familial cases and from cases' relatives. Medical confirmation was sought for all relatives reported to have had melanoma. The final sample comprises 15,907 persons in the 1,912 families of 2,118 melanoma cases, including 509 families in which there are two or more individuals with confirmed melanoma. Melanoma history and risk factors were obtained for 9,746 relatives, including 94 twins of cases. This is the largest family and twin study of cutaneous melanoma yet conducted in an unselected, geographically-defined population. We describe the design of the study and the characteristics of the total study population.

The classification of malignant melanoma, its histological reporting and registration: a revision of the 1972 Sydney classification.

A group of pathologists with an interest in malignant melanoma met in Sydney in 1982 to update the classification of melanoma formulated in Sydney in 1972. The group recommended that malignant melanoma be classified as follows: malignant melanoma with an adjacent component of superficial spreading type, malignant melanoma with an adjacent component of lentigo maligna type, malignant melanoma with an adjacent component of acral lentiginous type, malignant melanoma with an adjacent component of mucosal lentiginous type, malignant melanoma with no adjacent component, malignant melanoma of unclassifiable histogenetic type. The data recorded in the surgical pathology report should include: diagnosis of primary malignant melanoma, histogenetic classification, presence/absence of ulceration, micrometer-measured thickness, microanatomical level, mitotic rate/mm2, presence/absence of vascular invasion, presence/absence of regression, completeness of resection. The recommendations for the examination of specimens and the recording of data for research purposes and for tumour registries are described.

Smoking, chewing and drinking in Ban Pong. Northern Thailand.

The unusual pattern of oral cavity and respiratory tract cancers in Chiang Mai Province, Northern Thailand led to this descriptive study of smoking, drinking and chewing in a rural community in Chiang Mai Province. A high proportion of adults were smokers and both males and females had very high estimated lifetime tobacco tar exposures. Variation in additive mixed with tobacco in traditional cigars and differences in smoking may be related to different respiratory cancer patterns in males and females. Manufactured cigarettes were little smoked, and then mainly by young men and those of higher socioeconomic status. Betel nut chewing, found commonly in other parts of S.E. Asia was found only among the old, but chewing of miang, a fermented tea-leaf preparation was common in all age groups, and was generally accompanied by smoking. Drinking of alcoholic beverages was rare and infrequent.

Body site specific incidence of basal and squamous cell carcinoma in an exposed population, Townsville, Australia.

Most data on body site distribution of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) do not take into account the surface proportion occupied by body sites experiencing differing amounts of ultraviolet radiation. The recording of BCC and SCC is heterogenous and body sites are not standardized. This study was undertaken to assess the magnitude of the incidence rates of skin cancers at different body sites in a population which experiences high ultraviolet exposure and involved all primary care services in Townsville over 6 weeks in June 1993. The annual site-specific age-standardized (World Population) incidence rates of histologically diagnosed lesions, determined from data where lesions were recorded on a body map, were adjusted for surface area and expressed per 100,000 body units (BU). Relative site densities of lesions were also calculated. Annual incidence rates for BCC per 100,000 BU on the most exposed face (ears, nose and cheeks) were 25,893 (95% confidence interval (c.i.) 18,837-32,950), 13,222 (95% c.i., 8273-18,171) on the less exposed face (forehead,eyebrow, chin and jaw) and 27,837 (95% c.i., 12,560-43,115) on the least exposed face (area within the orbit and nasolabial fold). Incidence rates for SCC rates were highest on the less exposed face, 5843 (95% c.i., 2627-9058) most exposed face, 4200 (95% c.i., 1274-7126) and the exposed upper limb, 3786 (95% c.i., 2783-4789). The relative site density of histologically confirmed BCC was 14 on the most exposed face in males compared with 5 in females and 11 around the eyes (least exposed) in males and 9 in females compared with the body as a whole. Adjustment for body surface proportion demonstrates that highly exposed body sites are at very high risk. The magnitude of the incidence rates on these sites is attributed to the combination of a susceptible population and high ambient ultraviolet radiation (UVR).

Health beliefs and Pap smears among Thai women in Brisbane, Australia.

Although a number of studies have assessed the use of Pap smear among Thai women in Thailand, little is known about factors influencing the use of this cervical cancer screening among potentially high risk Thai migrant women. We related health belief model (HBM) factors and sociodemographic variables to the use of Pap smears among migrant Thai women in Brisbane, Australia. A cross-sectional study was conducted in Brisbane, Queensland, Australia. A snowball sampling method was used to recruit 145 women. Thirty-nine percent reported regular Pap smears. Summary HBM index and self-efficacy index were positively associated with Pap smears. Barriers to screening were negatively associated. The HBM appears to be a useful framework for planning cervical cancer prevention. Strategies that reduce barriers to the screening and increase the confidence of women and their self-efficacy are likely to increase their participation.

Possible aetiology of oral cancer in Papua New Guinea.

Oral cancer is the most common cancer seen in Papua New Guinea. Although there is a broad geographical correlation with betel chewing, there have been no analytical epidemiological studies and the aetiology remains poorly understood. A greater understanding of several putative risk factors and how they may interact is needed prior to any attempt to modify traditional customs. Although current strategies for primary prevention in India are based on the assumption that the risk of betel chewing is related to the tobacco in the quid, this cannot explain oral cancer in Papua New Guinea. In the latter, special epidemiological and laboratory investigations are needed to provide a scientific basis for future prevention.