Strength training improves the steadiness of slow lengthening contractions performed by old adults.

When old adults participate in a strength-training program with heavy loads, they experience an increase in muscle strength and an improvement in the steadiness of submaximal isometric contractions. The purpose of this study was to determine the effect of light- and heavy-load strength training on the ability of old adults to perform steady submaximal isometric and anisometric contractions. Thirty-two old adults (60-91 yr) participated in a 4-wk training program of a hand muscle. Both the light- and heavy-load groups increased one-repetition maximum and maximal voluntary contraction (MVC) strength and experienced similar improvements in the steadiness of the isometric and shortening and lengthening contractions. The increase in MVC strength was greater for the heavy-load group and could not be explained by changes in muscle activation. Before training, the lengthening contractions were less steady than the shortening contractions with the lightest loads (10% MVC). After training, there was no difference in steadiness between the shortening and lengthening contractions, except with the lightest load. These improvements were associated with a reduced level of muscle activation, especially during the lengthening contractions.     

Rhythmic processing in children with developmental dyslexia: auditory and motor rhythms link to reading and spelling.

Potential links between the language and motor systems in the brain have long attracted the interest of developmental psychologists. In this paper, we investigate a link often observed (e.g., [Wolff, P.H., 2002. Timing precision and rhythm in developmental dyslexia. Reading and Writing, 15 (1), 179-206.] between motor tapping and written language skills. We measure rhythmic finger tapping (paced by a metronome beat versus unpaced) and motor dexterity, phonological and auditory processing in 10-year old children, some of whom had a diagnosis of developmental dyslexia. We report links between paced motor tapping, auditory rhythmic processing and written language development. Motor dexterity does not explain these relationships. In regression analyses, paced finger tapping explained unique variance in reading and spelling. An interpretation based on the importance of rhythmic timing for both motor skills and language development is proposed.     

Age-related changes in hand grip strength among rural and urban Haryanvi Jat females

The aim of this study was to investigate the age-related changes in hand grip strength (both right and left hand) among rural and urban Jat females and its correlation with various anthropometric variables. The present cross-sectional study was based on a sample of 600 Jat females (rural=300, urban=300), ranging in age from 40 to 70 years. Findings indicated that rural and urban Jat females exhibit an age-related decline in the mean values of hand grip strength (both right and left hand). The comparison suggested that rural Jat females had significantly higher overall mean value of hand grip strength (kg) (right hand=20.35 vs 18.87, p<0.001 and left hand=17.05 vs 15.68, p<0.001) than their urban counterparts. Mean values for right hand grip strength were found to be higher than left hand grip strength in rural as well as urban Jat females. Significant and positive correlation coefficients exist between hand grip strength (both right and left hand) and various anthropometric variables (height, weight, body mass index, biceps and triceps skinfold thickness) in both rural and urban Jat females. An age-related decline in manual functioning of rural and urban Jat females may be attributed to behavioral factors (reduced physical activity, sedentary lifestyle) and poor nutrition (deteriorating quality and quantity of food intake with increasing age) associated with the normal aging process.     

Seropositivity for CMV and IL-6 levels are associated with grip strength and muscle size in the elderly

Background

Sarcopenia is an important cause of morbidity and mortality in older adults, with immunosenescence and inflammation being possible underlying mechanisms. We investigated the relationship between latent cytomegalovirus (CMV) infection, Interleukin 6 (IL-6) levels, muscle size and strength in a group of healthy older community-dwelling people.

Methods

Participants were healthy volunteers from the Lothian Birth Cohort 1936 study. Participants had IL-6 level and CMV antibody titre measured at age 70 years and grip strength and a volumetric T1-weighted MRI brain scan (allowing measurement of neck muscle cross-sectional area (CSA)) at age 73. Markers of childhood deprivation were adjusted for in the analysis due to correlations between childhood deprivation and latent CMV infection.

Results

866 participants were studied; 448 men (mean age 72.48 years, sd 0.70) and 418 women (mean age 72.51 years, sd 0.72). In men, CMV seropositivity was associated with smaller neck muscle CSA (p = 0.03, partial eta squared = 0.01), even after adjustment for IL-6 levels. Neck muscle CSA was not associated with CMV seropositivity in women, or CMV antibody titre or IL-6 level in either sex. Grip strength associated negatively with IL-6 level (right grip strength p<0.00001, partial eta squared 0.032 and left grip strength p<0.00001, partial eta squared 0.027) with or without adjustment for CMV serostatus or antibody titre. CMV status and antibody titre were not significantly associated with grip strength in either hand.

Conclusion

These findings support the hypothesis that there is a relationship between markers of immunosenescence (i.e. CMV serostatus and IL6 level) and low muscle mass and strength and longitudinal studies in older cohorts are now required to investigate these relationships further.

     

The influence of anthropometric characteristics to the handgrip and pinch strength in 6-10-year old children

The aim of the study was to investigate the relationships between handgrip and pinch strength values with basic body (body height, body mass, BMI) and with specific hand anthropometric parameters (fingers spans, lengths and perimeters) in prepubertal children. Body height, body mass and five fingers spans, lengths and perimeters were measured in 461 6-10 year old Estonian children according to Visnapuu & Jürim?e (2007). BMI was calculated (kg/m2). The maximal handgrip strength of the right and left hand was measured with hand dynamometer. The right and left key and tip pinch were measured with a pinch gauge. Body height, as a rule, in combination with BMI, was the strongest predictor of handgrip strength, especially in older children (about 40-60 % of the total variance, R2 x 100). From the hand anthropometry, the most important span parameter was FS2 (see explanations in the methods), which explained about 10-50% (R2 x 100) of the total variance. In older groups, the FS1 and FS3 were added to the models. From the length parameters, the most important was IFL, which in younger groups together with MFL explained 10-30% of the total variance, and in older groups the addition of RFL increased the influence to 45% (R2 x 100). From the perimeters, the most important one was P2 which explained the variability of the handgrip strength in younger groups by 15-30% (R2 x 100) and in older groups together with P3 and P4 even 30-40%. In children, the basic anthropometric parameters (body height and BMI) contribute more to the prediction of handgrip strength than the specific anthropometric parameters. With increasing age the contribution of basic and specific hand anthropometry increases and the relation between anthropometry and handgrip strength is stronger in boys compared with girls. The relation of basic and hand anthropometry to the tip and key pinch strength is relatively low.     

Age-specific correlation analysis of longitudinal physical fitness levels in men.

This study investigated the age-specific tracking of adult health- and performance-related fitness scores. In addition, the independent contribution of adolescent physical characteristics to the explanation of adult fitness scores was also studied. The sample consisted of 173 adults observed at age 30 years. These subjects had been followed at annual intervals from age 13 to age 18 years and were remeasured at age 30 years. At each age nine fitness tests were administered together with the recording of anthropometric dimensions, biological maturation, sports participation and family characteristics. Tracking was measured by the inter-age correlations at each age between 13 and 18 years and the performance scores at 30 years. The independent contribution of characteristics observed during adolescence to the explanation of adult fitness was investigated through stepwise multiple regression analysis and discriminant analysis with the adult fitness scores as the dependent variables and the fitness, maturation, anthropometric characteristics, sports participation and family background as the independent variables. Tracking between age 13 and age 30 years was moderately high (46% of variance explained) for flexibility, low to moderate (between 19% and 27% of variance explained) for the other fitness parameters and low for pulse recovery and static strength (7% to 11% of variance explained). Between age 18 and age 30 years the tracking was high for flexibility, moderately high for explosive and static strength, and moderate for the other fitness parameters except for pulse recovery. The amount of variance of adult fitness levels explained increased significantly when other characteristics observed during adolescence entered the regressions or discriminant functions.(ABSTRACT TRUNCATED AT 250 WORDS)     

The strength-dexterity test as a measure of dynamic pinch performance

We have developed a method to quantify the dynamic interaction between fingertip force magnitude (strength) and directional control (dexterity) during pinch with a novel strength-dexterity (S-D) test based on the principle of buckling of compression springs. The test consists of asking participants to use key and opposition pinch to attempt to fully compress springs, in random order, with a wide range of combinations of strength and dexterity requirements. The minimum force required to fully compress the spring and the propensity of the spring to buckle define the strength and dexterity requirements, respectively. The S-D score for each pinch style was the sum of the strength values of all springs successfully compressed fully. We tested 3 participant groups: 18 unimpaired young adults (40yr), and 14 adults diagnosed with carpo-metacarpal osteoarthritis (CMC OA) (>or = 36yr). We investigated the repeatability of the S-D test with 74 springs by testing 14 young adults twice on different days. The per-spring repeatability across subjects was >or = 94%. A minimum performance score for young adults was found as they all could compress a subset of 39 springs. Using this subset of springs, we compared the ability of the S-D score vs. maximal pinch force values to distinguish unimpaired hands from those with CMC OA of the thumb. The score for this 39-spring S-D test distinguished between CMC OA and asymptomatic older adults, whereas pinch meter readings did not (p<0.05). We conclude that the S-D test is repeatable and applicable to clinical research. We propose including the S-D test in studies aiming to quantify impairment and compare treatment outcomes in orthopaedic and neurological afflictions that degrade dynamic manipulation.     

Comparison of grip strength and isomeric endurance between the right and left hands of men and their relationship with age and other physical parameters.

Maximum handgrip strength and endurance of fatiguing isometric handgrip muscle contraction at 40% of maximum voluntary contraction of the dominant hand were assessed separately for both right and left hands of 99 right-handed men aged 7-73 years. Subjects below 10 years (n = 6) could not follow up the endurance test methods and were excluded. The relationship of handgrip strength and endurance with age and other physical parameters was also assessed. Maximum grip strength and endurance of fatiguing submaximal contraction of the right hand were significantly greater than that of the left hand for most age groups. Grip strength was positively correlated with age from 7-19 years (r = 0.94 for right and r = 0.89 for left) and was negatively correlated with age from 20-73 years (r = -0.74 right and r = -0.69 left). Grip strength was positively correlated with the weight (r = 0.86 right and r = 0.87 left), height (r = 0.88 right and r = 0.87 left) and body surface area (r = 0.9 for both) of the subjects. Endurance of contraction of both hands did not show any relationship with age, different physical parameters or grip strength of the subjects.     

Grip strength, muscle fatigue, and body composition in nomadic Turkana pastoralists

Tests of hand grip strength and hand grip muscle fatigue were conducted on Ngisonyoka Turkana pastoralists of northwest Kenya to explore some of the functional relationships between activity and body composition. The test of maximal voluntary contraction (MVC) of hand grip flexors was conducted on 151 Turkana and 38 U.S. men and women. The fatigue test was conducted on the same number of subjects who were instructed to attempt to maintain 80% of the MVC for 90 seconds. The results of these tests, combined with arm measurements of size and body composition, were used to evaluate muscle size and strength relationships and to estimate muscle fiber type distribution in the forearm. MVC values of Turkana men were low by U.S. and European standards. The low values resulted from smaller Turkana muscle areas. MVC values of Turkana women were comparable to those of U.S. and European women, reflecting comparable muscle areas. The fatigue curves of Turkana and U.S. men and women suggest that slow-twitch aerobic muscle fibers predominate for the hand grip flexors of the Turkana pastoralists.     

Effect of grip strength and grip strengthening exercises on instantaneous bat velocity of collegiate baseball players

Bat velocity is considered to be an important factor for successful hitting. The relationship between grip strength and bat velocity has not been conclusively established. The purposes of this study were to determine the relationship of grip strength to bat velocity and to ascertain whether the performance of resistance training exercises designed to specifically target the forearms and grip would significantly alter bat velocity. The subjects for this study were 23 male members (mean +/- SD, age = 19.7 +/- 1.3 years, height = 182.5 +/- 5.9 cm, weight = 85.4 +/- 15.5 kg, experience = 14.4 +/- 1.7 years) of a varsity baseball team at a National Collegiate Athletic Association Division II school. The Jamar hand dynamometer was used to test grip strength, and the SETPRO Rookie was used to measure instantaneous bat velocity at the point of contact with the ball. Subjects were randomly divided into an experimental group and a control group. For 6 weeks, both groups participated in their usual baseball practice sessions, but the experimental group also performed extra forearm and grip strengthening exercises, whereas the control group did not. Pretest and posttest correlations between grip strength and bat velocity revealed no significant relationship between grip strength and bat velocity (pretest r = 0.054, p = 0.807; posttest r = 0.315, p = 0.145). A dependent t-test performed on all subjects revealed that a significant (p = 0.001) increase in bat velocity did occur over the course of the study. A covariate analysis, employing pretest bat velocity as the covariate, revealed no significant difference (p = 0.795) in posttest bat velocity scores between the experimental and control groups. Thus, increases in bat velocity occurred, but the differences were similar for both the experimental and control groups. The findings of this study suggest that grip strength and bat velocity are not significantly related, and that the allocation of time and energy for added training of the forearms in order to improve grip strength for the purpose of increasing bat velocity may not be warranted.     

Low serum selenium concentrations are associated with poor grip strength among older women living in the community

Aging is associated with a loss of muscle strength, and, in turn, loss of muscle strength has been associated with increased risk of frailty, disability and mortality. The factors that contribute to loss of muscle strength with aging have not been well characterized. Selenium is important in normal muscle function because of its role in selenoenzymes that protect muscle against oxidative damage. We hypothesized that low serum selenium concentrations were associated with poor grip strength. We examined the association between serum selenium and hand grip strength among 676 moderately to severely disabled community-dwelling women in the Women's Health and Aging Study I in Baltimore, Maryland. After adjusting for age, race, body mass index, Mini-Mental Status Examination score, current smoking, hypertension, congestive heart failure and depression, serum selenium was associated with grip strength (P=0.04). This study supports the idea that selenium is important to muscle strength in older women.     

Influence of puberty on muscle development at the forearm

Despite its fundamental importance for physical development, the growth of the muscle system has received relatively little consideration. In this study, we analyzed the relationship between cross-sectional area (CSA) of forearm muscles and maximal isometric grip force with age and pubertal stage. The study population comprised 366 children, adolescents, and young adults from 6 to 23 yr of age (185 female) and 107 adults (88 female) aged 29 to 40 yr. By use of peripheral quantitative computed tomography, muscle CSA was determined at the site of the forearm, whose distance to the ulnar styloid process corresponded to 65% of forearm length. Both muscle CSA and grip force were higher in prepubertal boys than in girls. The gender differences decreased until pubertal stage 3 and reincreased thereafter. In girls at pubertal stage 5, muscle CSA no longer increased with age (P > 0.4), whereas there was still some age-related increase in grip force (P = 0.02). In boys at pubertal stage 5, both muscle CSA and grip force continued to increase significantly with age (P < 0.005 each). Specific grip force (grip force per muscle CSA) adjusted for forearm length increased by almost one-half between 6 and 20 yr of age, with no difference between the genders. In conclusion, forearm muscle growth takes a gender-specific course during puberty, indicating that it is influenced by hormonal changes. However, the increase in specific grip force is similar in both genders and thus appears to be independent of sex hormones.     

Alteration of period and amplitude of circadian rhythms in shift workers. With special reference to temperature, right and left hand grip strength

48 male shift workers in various industries volunteered to document circadian rhythms in sleeping and working, oral temperature, grip strength of both hands, peak expiratory flow and heart rate. All physiological variables were self-measured 4 to 5 times a day for 2 to 4 weeks. Individual time series were analyzed according to several statistical methods (power spectrum, cosinor, chi squares, ANOVA, correlation, etc.) in order to estimate rhythm parameters such as circadian period (tau) and amplitude (A), and to evaluate subgroup differences with regard to tolerance to shift work, age, duration of shift work, speed of rotation and type of industry. The present study confirms for oral temperature and extends to other variables (grip strength of both hands, heart rate) that intolerance to shift work is frequently associated with both internal desynchronization and small circadian amplitude. The internal desynchronization among several circadian rhythms supports the hypothesis that these latter are driven by several oscillators. Many differences were observed between circadian rhythms in right and left hand grip strength: circadian tau in oral temperature was correlated with that in the grip strength of the dominant hand but not with that of the other hand; changes in tau s of the non-dominant hand were age-related but did not correlate with temperature tau; only the circadian A of the non-dominant hand was associated with a desynchronization. Thus, circadian rhythms in oral temperature and dominant hand grip strength may be driven by the same oscillator while that of the non-dominant hand may be governed by a different one. Internal desynchronization between both hand grip rhythms as well as desynchronization of performance rhythms reported by others provide indirect evidence that circadian oscillator(s) may be located in the human cerebral cortex.     

Tactile spatial acuity in elderly persons: assessment with grating domes and relationship with manual dexterity

In this study, we sought to better define the limit of spatial resolution at the fingertips of elderly participants (n = 30, age 60-95 years) using an extended set of JVP grating domes, incorporating four new grating dimensions (2.5-, 3.5-, 4.0- and 4.5-mm width). A secondary aim was to examine whether deficits in tactile acuity could be related to hand dysfunction in older adults. Spatial resolution thresholds were determined by the finest grating whose orientation (dominant index finger) could be reported reliably. Manual dexterity was assessed with the Grooved Pegboard Test (GPT). The extended set of domes improved threshold measurements in a majority of participants (21/30). Still, accurate threshold estimates could not be obtained in one third of the participants, mostly in the older age group (8/9, 74-95 years). Grating resolution thresholds at the index finger were strongly correlated (r = 0.66, p<0.01) with dexterity scores derived from the GPT. From these results, we conclude that the 2.5- and 3.5-mm grating domes are suitable additions when assessing spatial acuity at the fingertips of older subjects between 60 and 70 years of age (mean threshold, 2.7+/-0.6 mm). For the older ones, the 4.0- and 4.5-mm domes can improve threshold measurements but interpretation of values can be complicated by the presence of undiagnosed pathologies (e.g., diffuse polyneuropathy) as people advance in age. The strong relationship between grating resolution thresholds and dexterity scores indicates that an impaired spatial acuity at the fingertips may translate into great difficulties in tasks requiring fine manipulations. These findings have important implications for the assessment of hand function in older adults.     

Anthropometric and strength variables to predict freestyle performance times in elite master swimmers

The aims of this study were to determine in elite master swimmers of both genders whether, using anthropometric variables and the hand grip strength measure, it was possible to predict freestyle performance time, whether the considered predictors were related similarly to different events (50, 100, 200, 400, 800 m), and whether they were the same in male and female master swimmers. The relationships between performance times and age, body mass, height, arm length, forearm length, forearm muscle volume, and hand grip strength were examined in 135 elite master swimmers. Pearson's simple correlation coefficients were calculated and then prediction equations were developed. Age, height, and hand grip strength were the best predictors in short-distance events, whereas only age and height were predictors in middle- and long-distance events. The corresponding coefficient of determination (R) of performance times were 0.84 in the 50-m event, 0.73 in the 100-m event, 0.75 in the 200-m event, 0.66 in the 400-m event, and 0.63 in the 800-m event. These regression equations were then cross-validated in a control group of 126 nonelite, age-matched swimmers, obtaining significant and good correlations for all distances (range, r = 0.67 and 0.83; p < 0.01), indicating that predictors are valid in an extended sample of master swimmers. Differences between sexes were not found in 50-m event, but were present in all other events. These models might be useful to determine individual performance times by contributing to improving the individual's training program and the selection of master swimmers. Coaches could have better accuracy in determining whether an athlete needs a strength training program in order to optimize performance time.     

Understanding the Relationship between Type 2 Diabetes Mellitus and Falls in Older Adults: A Prospective Cohort Study

Background

Older adults with type 2 Diabetes Mellitus are at increased risk of falling. The current study aims to identify risk factors that mediate the relationship between diabetes and falls.

Methods

199 older adults (104 with diabetes and 95 healthy controls) underwent a medical screening. Gait (GAITRite®), balance (AccuGait® force plate), grip strength (Jamar®), and cognitive status (Mini-Mental State Examination and Clock Drawing Test) were assessed. Falls were prospectively recorded during a 12-month follow-up period using monthly calendars.

Results

Compared to controls, diabetes participants scored worse on all physical and cognitive measures. Sixty-four participants (42 diabetes vs. 22 controls) reported at least one injurious fall or two non-injurious falls (“fallers”). Univariate logistic regression identified diabetes as a risk factor for future falls (Odds Ratio 2.25, 95%CI 1.21–4.15, p = 0.010). Stepwise multiple regressions defined diabetes and poor balance as independent risk factors for falling. Taking more medications, slower walking speed, shorter stride length and poor cognitive performance were mediators that reduced the Odds Ratio of the relationship between diabetes and faller status relationship the most followed by reduced grip strength and increased stride length variability.

Conclusions

Diabetes is a major risk factor for falling, even after controlling for poor balance. Taking more medications, poorer walking performance and reduced cognitive functioning were mediators of the relationship between diabetes and falls. Tailored preventive programs including systematic medication reviews, specific balance exercises and cognitive training might be beneficial in reducing fall risk in older adults suffering from diabetes.     

The contribution of prenatal environment and genetic factors to the association between birth weight and adult grip strength

Low birth weight has been associated with reduced hand grip strength, which is a marker of future physical function and disease risk. The aim of this study was to apply a twin pair approach, using both ‘individual’ data and ‘within-pair’ differences, to investigate the influence of birth weight on hand grip strength and whether this association may be mediated through fat free mass (FFM). Participants from the East Flanders Prospective Twin Survey were included if born without congenital abnormalities, birth weight >500 g and ≥22 weeks of gestation. Follow up in adulthood (age: 18–34 year), included anthropometric measures and hand grip (n = 783 individuals, n = 326 same-sex twin pairs). Birth weight was positively associated with hand grip strength (β = 2.60 kg, 95% CI 1.52, 3.67, p<0.001) and FFM (β = 4.2, 95% CI 3.16, 5.24, p<0.001), adjusted for gestational age, sex and adult age. Using ‘within-pair’ analyses, the birth weight hand grip association was significant in DZ men only (β = 5.82, 95% CI 0.67, 10.97, p = 0.028), which was attenuated following adjustment for FFM. Within-pair birth weight FFM associations were most pronounced in DZ men (β = 11.20, 95% CI 7.18, 15.22, p<0.001). Our ‘individual’ analyses show that higher birth weight is associated with greater adult hand grip strength, which is mediated through greater adult FFM. The ‘within-pair’ analyses confirm this observation and furthermore show that, particularly in men, genetic factors may in part explain this association, as birth weight differences in DZ men result in greater differences in adult strength and FFM.     

Musculoskeletal capacity of employees aged 44 to 58 years in physical, mental and mixed types of work

The musculoskeletal capacity of 60 women and 69 men, average age 52.3 +/- 3.7 years was determined, including measurements of anthropometry, maximal isometric trunk flexion and extension, sit-ups, isometric hand grip strength and back mobility. According to the job and to cluster analysis, the subjects were divided into three dominating work groups; physical, mental, and mixed groups. The results showed significant differences in right hand grip strength of the women and in the number of sit-ups by men among the three work groups (p less than 0.05). The differences between the other tests were not significant, although the physical group in the women and either the physical or the mixed group in the men had systematically the lowest mean values in almost all tests. It is concluded that jobs with mainly physical demands do not guarantee superior musculoskeletal capacity in older employees.     

Hormone therapy in postmenopausal women affects hemispheric asymmetries in fine motor coordination

Evidence exists that the functional differences between the left and right cerebral hemispheres are affected by age. One prominent hypothesis proposes that frontal activity during cognitive task performance tends to be less lateralized in older than in younger adults, a pattern that has also been reported for motor functioning. Moreover, functional cerebral asymmetries (FCAs) have been shown to be affected by sex hormonal manipulations via hormone therapy (HT) in older women. Here, we investigate whether FCAs in fine motor coordination, as reflected by manual asymmetries (MAs), are susceptible to HT in older women. Therefore, sixty-two postmenopausal women who received hormone therapy either with estrogen (E) alone (n = 15), an E-gestagen combination (n = 21) or without HT (control group, n = 26) were tested. Saliva levels of free estradiol and progesterone (P) were analyzed using chemiluminescence assays. MAs were measured with a finger tapping paradigm consisting of two different tapping conditions. As expected, postmenopausal controls without HT showed reduced MAs in simple (repetitive) finger tapping. In a more demanding sequential condition involving four fingers, however, they revealed enhanced MAs in favour of the dominant hand. This finding suggests an insufficient recruitment of critical motor brain areas (especially when the nondominant hand is used), probably as a result of age-related changes in corticocortical connectivity between motor areas. In contrast, both HT groups revealed reduced MAs in sequential finger tapping but an asymmetrical tapping performance related to estradiol levels in simple finger tapping. A similar pattern has previously been found in younger participants. The results suggest that, HT, and E exposure in particular, exerts positive effects on the motor system thereby counteracting an age-related reorganization.     

Partitioning additive genetic variance into genomic and remaining polygenic components for complex traits in dairy cattle

ABSTRACT: BACKGROUND: Low cost genotyping of individuals using high density genomic markers were recently introduced as genomic selection in genetic improvement programs in dairy cattle. Most implementations of genomic selection only use marker information, in the models used for prediction of genetic merit. However, in other species it has been shown that only a fraction of the total genetic variance can be explained by markers. Using 5217 bulls in the Nordic Holstein population that were genotyped and had genetic evaluations based on progeny, we partitioned the total additive genetic variance into a genomic component explained by markers and a remaining component explained by familial relationships. The traits analyzed were production and fitness related traits in dairy cattle. Furthermore, we estimated the genomic variance that can be attributed to individual chromosomes and we illustrate methods that can predict the amount of additive genetic variance that can be explained by sets of markers with different density. RESULTS: The amount of additive genetic variance that can be explained by markers was estimated by an analysis of the matrix of genomic relationships. For the traits in the analysis, most of the additive genetic variance can be explained by 44 K informative SNP markers. The same amount of variance can be attributed to individual chromosomes but surprisingly the relation between chromosomal variance and chromosome length was weak. In models including both genomic (marker) and familial (pedigree) effects most (on average 77.2%) of total additive genetic variance was explained by genomic effects while the remaining was explained by familial relationships. CONCLUSIONS: Most of the additive genetic variance for the traits in the Nordic Holstein population can be explained using 44 K informative SNP markers. By analyzing the genomic relationship matrix it is possible to predict the amount of additive genetic variance that can be explained by a reduced (or increased) set of markers. For the population analyzed the improvement of genomic prediction by increasing marker density beyond 44 K is limited.