Cartilaginous endplate avulsion is associated with modic changes and endplate defects, and residual back and leg pain following lumbar discectomy.

OBJECTIVE: While cartilaginous endplate (CEP) avulsion is a common finding in discectomy due to lumbar disc herniation, its roles in residual back and leg pain, associations with Modic changes (MCs) and endplate defects (EPD) remain unknown. DESIGN: Patients with a single-level lumbar disc herniation who underwent endoscopic discectomy were studied. On MR images, the adjacent endplates of the herniated disc were assessed for MCs and EPD. The presence of CEP avulsion was examined under endoscopic and visualized inspection. Back and leg pain were evaluated by a numeric rating scale (NRS) and the Oswestry Disability Index. Associations of CEP avulsion with adjacent MCs, EPD, and residual back and leg pain were examined. In addition, histological features of avulsed CEP were determined using gross staining and immunohistochemical methods. RESULTS: A total of 386 patients were included. CEP avulsion was found in 166 (43%) patients, and adjacent MCs and EPD were observed in 117 (30.3%) and 139 (36%) patients. The presence of CEP avulsion was associated with greater age, adjacent MCs (OR = 2.60, 95%CI [1.61-4.19]) and EPD (OR = 1.63, 95%CI [1.03-2.57]). Among the 187 patients with ≥2 years follow-up, CEP avulsion was associated with residual back pain (OR = 2.49, 95%CI [1.29-4.82]) and leg pain (OR = 2.25, 95%CI [1.04-4.84]). Histologically, the avulsed CEP was characterized by multiple defects, apparent inflammation, and nucleus invasion, as well as the upregulation of IL-1ß, caspase-1, and NLRP3 inflammasome. CONCLUSION: CEP avulsion was associated with MCs, EPD, and residual back and leg pain after discectomy, which may be attributed to NLRP3 inflammasome related inflammations.

Ageing workers with work-related musculoskeletal injuries.

BACKGROUND: Older workers often take longer to recover and experience more missed workdays after work-related injuries, but it is unclear why or how best to intervene. Knowing the characteristics of older injured workers may help in developing interventions to reduce the likelihood of work disability. AIMS: To describe and compare several characteristics between younger and middle-aged working adults (25-54 years), adults nearing retirement (55-64 years) and adults past typical retirement (≥65 years), who sustained work-related musculoskeletal injuries. METHODS: In this cross-sectional study, Alberta workers' compensation claimants with subacute and chronic work-related musculoskeletal injuries were studied. A wide range of demographic, employment, injury and clinical characteristics were investigated. Descriptive statistics were computed and compared between the age groups. RESULTS: Among 8003 claimants, adults 65 years or older, compared to those 25-54 and 55-64 years, had lower education (16 versus 10 and 12%, P < 0.001) and were more likely to work in trades, transport and related occupations (50 versus 46 and 44%, P < 0.001), to have less offers of modified work (57 versus 39 and 42%, P < 0.001), more fractures (18 versus 14 and 11%, P < 0.001) and no further rehabilitation recommended after assessment (28 versus 18 and 20%, P < 0.01). CONCLUSIONS: Injured workers past typical retirement age appeared to be a disadvantaged group with significant challenges from a vocational rehabilitation perspective. They were less likely to have modified work options available or be offered rehabilitation, despite having more severe injuries.

Do variations in paraspinal muscle morphology and composition predict low back pain in men?

This longitudinal study aimed to clarify the longstanding controversy over whether variations in paraspinal muscle morphology (e.g., size, composition and asymmetry) are predictors of low back pain (LBP). A sample of 99 Finnish men were included in this population-based longitudinal study. Data were collected through a structured interview, physical examination and magnetic resonance imaging (MRI). Baseline measurements of the lumbar multifidus and erector spinae muscles were obtained from T2-weighted axial images at L3-L4 and L5-S1, and interview data were obtained at baseline, 1- and 15-year follow-ups. Few of the paraspinal muscle parameters investigated were predictors of change in LBP frequency, intensity or sciatica at 1- and 15-year follow-ups in the population-based sample, and findings were not consistent across muscles and spinal levels. However, greater multifidus and erector spinae fatty infiltration at L5-S1 was associated with a higher risk of having continued, frequent, persistent LBP at 1-year follow-up. None of the relationships observed was confounded by body mass index or the amount of physical activity at work or leisure. This longitudinal study provided evidence that variations in paraspinal muscle morphology on MRI have a limited, if not uncertain, role in the short- and long-term predictions of LBP in men.

Quantitative measurement of intervertebral disc signal using MRI.

AIM: To investigate the spinal cord as an alternative intra-body reference to cerebrospinal fluid (CSF) in evaluating thoracic disc signal intensity. MATERIALS AND METHODS: T2-weighted magnetic resonance imaging (MRI) images of T6-T12 were obtained using 1.5 T machines for a population-based sample of 523 men aged 35-70 years. Quantitative data on the signal intensities were acquired using an image analysis program (SpEx). A random sample of 30 subjects and intraclass correlation coefficients (ICC) were used to examine the repeatability of the spinal cord measurements. The validity of using the spinal cord as a reference was examined by correlating cord and CSF samples. Finally, thoracic disc signal was validated by correlating it with age without adjustment and adjusting for either cord or CSF. Pearson's r was used for correlational analyses. RESULTS: The repeatability of the spinal cord signal measurements was extremely high (>or=0.99). The correlations between the signals of spinal cord and CSF by level were all above 0.9. The spinal cord-adjusted disc signal and age correlated similarly with CSF-adjusted disc signal and age (r=-0.30 to -0.40 versus r=-0.26 to -0.36). CONCLUSION: Adjacent spinal cord is a good alternative reference to the current reference standard, CSF, for quantitative measurements of disc signal intensity. Clearly fewer levels were excluded when using spinal cord as compared to CSF due to missing reference samples.

Role of genetic and environmental influences on heart rate variability in middle-aged men.

Our aim was to estimate causal relationships of genetic factors and different specific environmental factors in determination of the level of cardiac autonomic modulation, i.e., heart rate variability (HRV), in healthy male twins and male twins with chronic diseases. The subjects were 208 monozygotic (MZ, 104 healthy) and 296 dizygotic (DZ, 173 healthy) male twins. A structured interview was used to obtain data on lifetime exposures of occupational loading, regularly performed leisure-time sport activities, coffee consumption, smoking history, and chronic diseases from 12 yr of age through the present. A 5-min ECG at supine rest was recorded for the HRV analyses. In univariate statistical analyses based on genetic models with additive genetic, dominance genetic, and unique environmental effects, genetic effects accounted for 31-57% of HRV variance. In multivariate statistical analysis, body mass index, percent body fat, coffee consumption, smoking, medication, and chronic diseases were associated with different HRV variables, accounting for 1-11% of their variance. Occupational physical loading and leisure-time sport activities did not account for variation in any HRV variable. However, in the subgroup analysis of healthy and diseased twins, occupational loading explained 4% of the variability in heart periods. Otherwise, the interaction between health status and genetic effects was significant for only two HRV variables. In conclusion, genetic factors accounted for a major portion of the interindividual differences in HRV, with no remarkable effect of health status. No single behavioral determinant appeared to have a major influence on HRV. The effects of medication and diseases may mask the minimal effect of occupational loading on HRV.

The influence of magnetic resonance imaging findings of degenerative disease on dual-energy X-ray absorptiometry measurements in middle-aged men.

PURPOSE: To examine degenerative features based on magnetic resonance imaging (MRI) measurements at the lumbar spine in relation to dual-energy X-ray absorptiometry (DXA), and to investigate whether bone mineral density (BMD) is reflected in the substitution of bone trabecular structure by fat at the vertebral body level indicated by MRI T1 relaxation time, endplate concavity, and hypertrophic (osteophytes and endplate sclerosis) MRI findings. MATERIAL AND METHODS: The sample for this cross-sectional study was composed of 102 subjects, 35-70 years old, from a population-based cohort. Data collection included DXA in the anterior-posterior projection at the L1-L4 vertebrae and right femoral neck, and MRI of the lumbar spine in the midsagittal plane. RESULTS: Age, vertebral signal intensity, osteophytes, and endplate concavity collectively explained 20% of the variance in spine BMD. CONCLUSION: The study findings suggest that degenerative findings based on MRI measurements at the lumbar spine have an influence on bone assessment using DXA. Therefore, an overall bone assessment such as DXA might not offer an accurate measure of BMD.

Genetic and constitutional influences on bone turnover markers: a study of male twin pairs.

Biochemical markers of bone turnover originating from type I procollagen synthesis or type I collagen breakdown were examined in men using a classic twin study design based on monozygotic (MZ) and dizygotic (DZ) twins. The aim was to estimate the influence of heredity (genes and shared family childhood elements) and constitutional factors in determining procollagen type I amino-terminal propeptide (PINP), type I collagen carboxy-terminal telopeptide (ICTP), and urinary amino-terminal type I collagen telopeptide (NTx) marker levels in a sample of in 98 MZ and 108 DZ male twin pairs. We are not aware of any prior studies conducted in men that address the influence of genetic factors on bone turnover marker variability. The findings support a dominant role for heredity in the variation of bone resorption marker levels in men, with additive genetic effects explaining two-thirds of the variance in the bone resorption markers NTx and ICTP. Genetic factors may contribute less for PINP, a marker of bone formation. The genetic loci influencing PINP or NTx and body weight/disc axial area, although related in part, appeared to be largely independent, indicating that genetic effects on bone turnover are unlikely to be to a large degree a result of genetic regulation of individual body weight.

Material handling performance of patients with chronic low back pain during functional capacity evaluation: a comparison between three countries.

PURPOSE: Functional Capacity Evaluations (FCEs) are batteries of tests designed to measure patients' ability to perform work-related activities. Although FCEs are used worldwide, it is unknown how patients' performances compare between countries or settings. This study was performed to explore similarities and differences in FCE performance of patients with chronic low back pain (CLBP) between three international settings that utilize the same FCE protocol. METHODS: Standardized FCEs were performed on three cohorts of patients with CLBP: A sample from an outpatient rehabilitation context in The Netherlands (n = 121), a Canadian sample in a Worker's Compensation context (n = 273), and a Swiss sample in an inpatient rehabilitation context (n = 170). Patients were undergoing FCE as part of their usual clinical care. Means and standard deviations of maximum performance on the FCE material handling items were calculated and differences compared using ANOVA. Multivariable linear regression was used to determine the relationship between country of origin and FCE performance while controlling for potential confounders including, age, sex, duration of back pain problems, and self-reported pain and disability ratings. RESULTS: Compared to the Dutch sample, the mean performance of patients in the Canadian and Swiss samples was consistently lower on all FCE items. This association remained statistically significant after controlling for potential confounders. CONCLUSIONS: Considerable differences were observed between settings in maximum weight handled on the various FCE items. Future FCE research should examine the effects of a number of potentially influential factors, including variability in evaluator judgements across settings, the evaluator-patient interaction and patients' expectations of the influence of FCE results on disability compensation.

The predictive role of bone turnover markers for BMD in middle-aged men.

Measurement of bone turnover markers has been proposed as a potentially valuable clinical laboratory aid in osteoporosis risk assessment. These markers may allow quantitative evaluation of rates of bone loss, and thereby identify persons at risk for osteoporosis at an earlier stage. As far as we know, this is the longest longitudinal study on bone turnover markers conducted in adult men. The objectives of this study were to determine whether markers of bone formation (type I procollagen amino-terminal propeptide, PINP, and carboxy-terminal propeptide, PICP), and of bone resorption (type I collagen carboxy-terminal telopeptide, ICTP), are predictive of changes in lumbar spine and femoral neck BMD over a 5-year period, and to determine the ability of the bone resorption marker urine amino-terminal telopeptide (NTx) to explain the variance in BMD change over the past 5 years in a group of men 35-69 years old. In this group, NTx was the only marker to correlate significantly with BMD changes at the femoral neck (r = -0.21), but not at the spine. The use of the biochemical markers studied to predict change in bone density in adult men in middle-aged years is of very limited value.

Does functional capacity evaluation predict recovery in workers' compensation claimants with upper extremity disorders?

OBJECTIVES: Functional capacity evaluations (FCEs) are commonly used to determine return-to-work readiness and guide decision making following work related injury, yet little is known of their validity. The authors examined performance on the Isernhagen Work Systems' FCE as a predictor of timely and sustained recovery in workers' compensation claimants with upper extremity disorders. A secondary objective was to determine whether FCE is more predictive in claimants with specific injuries (that is, fracture) as compared to less specific, pain mediated disorders (that is, myofascial pain). METHODS: The authors performed a longitudinal study of 336 claimants with upper extremity disorders undergoing FCE. FCE indicators were maximum performance during handgrip and lift testing, and the number of tasks where performance was rated below required job demands. Outcomes investigated were days receiving time-loss benefits (a surrogate of return to work or work readiness) in the year following FCE, days until claim closure, and future recurrence defined as whether benefits restarted, the claim reopened, or a new upper extremity claim was filed. Cox and logistic regression were used to determine the prognostic effect of FCE crudely and after controlling for potential confounders. Analysis was performed separately on claimants with specific and pain mediated disorders. RESULTS: Most subjects (95%) experienced time-loss benefit suspension within one year following FCE. The one year recurrence rate was 39%. Higher lifting performance was associated with faster benefit suspension and claim closure, but explained little variation in these outcomes (r2 = 1.2-11%). No FCE indicators were associated with future recurrence after controlling for confounders. Results were similar between specific injury and less specific groups. CONCLUSIONS: Better FCE performance was a weak predictor of faster benefit suspension, and was unrelated to sustained recovery. FCE was no more predictive in claimants with specific pathology and injury than in those with more ambiguous, pain mediated conditions.

Factors associated with exercise lifestyle--a study of monozygotic twins.

Regular exercise is widely advocated for a broad range of health issues. Yet, the association of familial factors (i. e. both genetic and childhood environmental factors) and specific environmental factors (not shared by family members) as well as health behavior with lifelong exercise participation is currently poorly understood. A total of 117 monozygotic male twin pairs aged 35 - 69 y (mean age 49 y), recruited from the population-based Finnish Twin Cohort, were studied. A summary outcome exercise variable was created by calculating the mean hours of exercise per week from 18 y of age to present from data provided from a structured interview. Suspected factors associated with exercise were analyzed with linear regression, while pairwise relationships were analysed using polychoric correlations and structural equation modeling. There was substantial familial aggregation in adulthood exercise, accounting for 43 % of all variation in exercise using the LISREL model. Factors associated with enhanced adherence to exercise in adulthood were participation in exercise and competitive sports in adolescence (from age 12 to 18). Education, age, number of chronic diseases, smoking, alcohol use, marital status, number of children and number of changes in residence were not associated with exercise adherence in adulthood. Our results suggest that early childhood environmental factors strongly influence exercise level throughout the lifespan. Therefore, interventions aimed at enhancing lifelong exercise participation may achieve more beneficial long-term results by targeting families and other childhood and adolescent environments.

Repeatability of lifetime exercise reporting.

The purpose of the study was to determine the reliability of lifetime exercise data obtained through a structured interview. Interviews were conducted in 1992-1993 and repeated in 1997 in 150 monozygotic male twins, aged 35-69 years, from the population-based Finnish Twin Cohort. Exercise mode, frequency, duration, intensity and period of participation were solicited for each regularly performed exercise from 12 years of age to the present. Questions related to the most common exercise mode reported in the initial interview were repeated in all subjects and the entire exercise interview was repeated in a subgroup of 38 subjects. The repeatability was highest for exercise years and mean hours/ week by mode for the most commonly performed exercise (Mean ICC=0.63-0.90), and for the sum of all lifetime exercises reported (Mean ICC = 0.69-0.73). The lowest repeatability was found for exercise intensity (Mean Kappa = 0.33-0.48). Similarly poor reliability was found for whether or not exercise was performed at a competitive level (Mean Kappa = 0.25-0.63). Overall, the structured interview of lifetime exercise was most repeatable for years of exercise and mean hours/week. Thus, these exposure variables should be considered in retrospective studies of exercise effects.

The relative roles of intragenic polymorphisms of the vitamin d receptor gene in lumbar spine degeneration and bone density.

STUDY DESIGN: A retrospective cohort study. OBJECTIVES: To compare the magnitudes of the associations of TaqI polymorphisms of the vitamin D receptor gene with bone density and lumbar spine degeneration in the same sample. SUMMARY OF BACKGROUND DATA: Vitamin D receptor gene variations are associated with osteoporosis, osteoarthritis, and disc degeneration. Their role in these conditions remains poorly understood. METHODS: Bone density of the spine and femur were determined through DEXA, and lumbar disc degeneration was determined from magnetic resonance imaging assessments of signal intensity, disc narrowing, bulging, anular tears, herniations, and osteophytes. Associations between these measures and TaqI polymorphisms of the coding region of the Vitamin D receptor locus were examined in a population-based sample of 142 men. RESULTS: The strongest associations were with signal intensity and anular tears, which were worse for the subjects with tt genotypes than for those with TT genotypes in the L4-S1 spine discs. Conversely, the prevalences of disc bulges and osteophytes were lowest for the tt genotype. Bone density, disc height, and herniations did not differ significantly by genotype. CONCLUSIONS: The strongest association of Vitamin D receptor TaqI polymorphisms with degeneration in nonmineralized connective tissues suggests that the underlying mechanism of TaqI polymorphisms is not specific to bone. This study demonstrated for the first time that those with the tt genotype had more anular tears than those with the TT genotype, a finding that should stimulate further analyses of this gene in conditions that result in back pain. The apparent discrepancies of the associations of the tt genotype with lower signal intensity and more anular tears, but less bulges and osteophytes, could be explained if bulging and osteophytes primarily represented remodeling related to lifetime physical loading.

Disc degeneration and bone density in monozygotic twins discordant for insulin-dependent diabetes mellitus.

The effects of insulin-dependent diabetes mellitus on bone density and connective tissue degeneration have theoretical interest and practical relevance. Several experimental studies in animals have demonstrated the harmful effects of insulin deficiency on connective tissues. However, clinical studies in humans have produced somewhat contradictory results, most likely due to difficulties controlling for general degeneration and factors associated with diabetes. In nine pairs of monozygotic twins discordant for insulin-dependent diabetes mellitus, we compared femoral and lumbar bone mineral density (assessed by dual-energy x-ray absorptiometry) and spinal degeneration (assessed by magnetic resonance imaging). The bone densities were, on average, 0.1-0.3% lower (p = 0.87-0.96) in diabetic patients. However, after controlling for smoking, we found that the bone density in the femoral neck was 2.5% (0.025 g/cm2) lower in diabetic individuals than in their twins (p = 0.09). The five magnetic resonance imaging parameters used to evaluate disc degeneration did not differ between diabetic patients and their twins. In conclusion, our results provide no evidence that insulin-dependent diabetes mellitus has any major effect on bone density or disc degeneration.

The influence of occupation on lumbar degeneration.

In many countries, back problems have been defined as occupational injuries. The belief underlying this injury model is that back symptoms are caused primarily by work-related mechanical factors that damage the structures of the spine, either through a single incident or repeated loading. Although the etiopathogenesis of degenerative findings in the disc and their relation to pain are poorly understood, changes in the disc are suspected of underlying many back symptoms. The focus of this article is on examining the relation between occupational factors and disc degeneration. Occupational factors suspected of accelerating spinal degeneration include accident-related trauma; heavy physical loading and materials handling, including lifting, bending, and twisting; prolonged sitting; and sustained nonneutral work postures and vehicular driving. There is evidence to suggest that occupational exposures have an effect on disc degeneration. However, these factors explain little of the variability in degeneration found in the adult population. Furthermore, the lack of a clear dose-response relation between time spent in various occupational loading conditions and degenerative findings adds to doubts about a strong causal link. The contribution of suspected occupational risk factors appears to be particularly modest when compared with familial influences, which reflect the combined effects of genes and early childhood environment. These findings challenge the dominant role assumed for occupational loading in disc degeneration and associated back problems, and suggest a more complex etiology.

Intragenic polymorphisms of the vitamin D receptor gene associated with intervertebral disc degeneration.

STUDY DESIGN: A study in genetic epidemiology of disc degeneration, based on lifetime exposure data, findings on magnetic resonance imaging, and genotyping of intragenic markers. OBJECTIVES: To pursue the potential correlation between common allelic variations in the vitamin D receptor locus and degeneration of the intervertebral disc. SUMMARY OF BACKGROUND DATA: Familial aggregation has been observed in intervertebral disc degeneration, but the relative significance of the genetic component and shared environmental influences is unknown. The identification of relevant candidate genes associated with disc degeneration would specify a genetic component and increase our understanding of the etiopathogenesis of disc degeneration. METHODS: From the population-based Finnish Twin cohort, 85 pairs of male monozygotic twins were selected based on exposure to suspected risk factors for disc degeneration. Interview data were gathered on relevant lifetime exposures, and thoracic and lumbar disc degeneration was determined through quantitative and qualitative assessments of signal intensity on magnetic resonance imaging, and qualitative assessments of disc bulging and disc height narrowing. Possible associations were examined between disc degeneration measures and two polymorphisms of the coding region of the vitamin D receptor locus. RESULTS: Two intragenic polymorphisms of the vitamin D receptor gene revealed an association with disc degeneration. Quantitatively assessed signal intensities of thoracic and lumbar (T6-S1) discs were 12.9% worse in men with the Taql tt genotype and 4.5% worse in men with the Tt genotype, compared with signal intensity in men with the TT genotype (age adjusted P = 0.003). A similar pattern was found between disc signal intensity and Fokl genotypes; men with the ff and Ff genotypes had mean signal intensities that were 9.3% and 4.3% lower, respectively, than those in men with FF genotypes (age-adjusted P = 0.006). The summary scores of qualitatively assessed signal intensity, bulging, and disc height were 4.0% and 6.9% worse in men with Ff and ff genotypes, respectively, when compared with those in men with the FF genotype (age-adjusted P = 0.029). CONCLUSION: Specific vitamin D receptor alleles were associated with intervertebral disc degeneration as measured by T2-weighted signal intensity, demonstrating for the first time, the existence of genetic susceptibility to this progressive, age-related degenerative process.

The effect of lifelong exercise on psychomotor reaction time: a study of 38 pairs of male monozygotic twins.

PURPOSE: The aim was to study the effect of lifetime physical activity on psychomotor speed. METHODS: Foot and dominant hand visual simple and choice psychomotor reaction times were studied among monozygotic twins (38 pairs) aged 35-69, discordant for lifetime exercise histories. RESULTS: There was a trend that some components of psychomotor reaction time were faster for frequent than for occasional exercisers, but the findings were not consistent for the hand and feet. After controlling for occupational physical activity, only choice decision time for the hand (26 ms, P < 0.01) and choice reaction time for the contralateral foot (51 ms, P < 0.05) both remained 7% faster. There was no trend for systematic differences in reaction times between twins engaged in regular exercise versus their siblings exercising infrequently. CONCLUSIONS: Results suggest a somewhat smaller effect of exercise than reported in previous studies. Reaction time may be significantly affected only by vigorous, frequent exercise. Thus, health promotion through exercise may be unlikely to have notable effects on reaction time.

Determinants of paraspinal muscle cross-sectional area in male monozygotic twins.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate the general magnitude and relative contributions of anthropometric, lifestyle, and medical history factors and familial aggregation (combined effects of genes and early environment) as determinants of paraspinal muscle cross-sectional area (CSA). SUBJECTS: The subjects were 65 pair of male monozygotic twins aged 35 to 65 years (mean = 49, SD = 8). METHODS: Study methods included magnetic resonance imaging, percentage body fat determination, and a detailed interview. RESULTS: Most of the anthropometric factors were associated with the CSAs. Familial aggregation was the strongest determinant, however, explaining 66% to 73% of the variance in the outcomes beyond what age alone predicted. Levels of occupational, sport, and leisure-time physical activities reported by the subjects had negligible effects. CONCLUSION AND DISCUSSION: The CSAs of the paraspinal muscles were influenced more by some combination of genes and early environmental factors than by anthropometric factors and lifestyle choices in adulthood.

Determinants of psychomotor speed among 61 pairs of adult male monozygotic twins.

BACKGROUND: Declining psychomotor speed is an indicator of the aging process, and it is influenced by genetics and environmental factors. The present study examined the relative effects of familial aggregation (reflecting a combination of genetics and early environmental influences), and occupational, lifestyle, and health factors on psychomotor speed. METHODS: Hand and foot psychomotor speed was studied with 61 pairs of monozygotic male twins aged 35-67 years from the population-based Finnish Twin Cohort. The determinants of visual simple and choice reaction times were analyzed with multiple regression analysis. RESULTS: Familial aggregation, reflecting genetic influences and shared environmental effects, explained in mean 47% of decision times, 31% of movement times, and 37% of response times (decision time and movement time combined). Age, cardiovascular morbidity, lifetime vigorous and frequent exercise participation, and mean lifetime daily hours sitting at work explained 0-19% of hand psychomotor speed and 0-10% of foot speed, depending on the outcome. The predicted increase in decision times due to the presence of cardiovascular morbidity was 11-35 ms. The predicted increase for hand and contralateral foot response times between ages 45 and 55 was 18-41 ms. Smaller effects were noted for each year of strenuous exercise and each hour/day of average lifetime sitting at work. CONCLUSIONS: Results indicate that cardiovascular status, age, strenuous exercise, and work play a role in psychomotor speed, but a rather minor one. In contrast, genetic and shared early environmental influences as revealed from familial aggregation were relatively strong, yet a major proportion of the variability in psychomotor speed remained unexplained.

Lifetime exercise and disk degeneration: an MRI study of monozygotic twins.

Participation in some competitive sports has been shown to increase disk degeneration; however, the long-term effects of recreational physical activities are unclear. We investigated the effects of endurance exercise and power sports on disk degeneration in monozygotic male twins with contrasting lifetime exercise histories. The effects of endurance exercise were studied in 22 discordant twin pairs (mean lifetime frequencies of 3.9 vs 1.1 times/wk), and the effects of power sports were investigated in 12 discordant pairs (2,300 vs 200 h of weightlifting). The age range of the twins was from 35 to 69 yr. No differences in MRI findings between co-twins discordant for endurance exercise were found at any of the spinal regions. Subjects with more power sport involvement had greater disk degeneration in the T6-T12 region (P < 0.03), but similar findings were not present in the lumbar spine. Controlling for recalled back injuries, occupational loading, smoking, and driving did not significantly affect the results. No signs of beneficial or harmful effects of lifetime endurance exercise on disk degeneration were seen. Increased power sport participation was associated with slightly greater disk degeneration in the lower thoracic spine, but not in the lumbar spine.