There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

The purpose of this Position Stand is to provide guidance to professionals who counsel and prescribe individualized exercise to apparently healthy adults of all ages. These recommendations also may apply to adults with certain chronic diseases or disabilities, when appropriately evaluated and advised by a health professional. This document supersedes the 1998 American College of Sports Medicine (ACSM) Position Stand, "The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults." The scientific evidence demonstrating the beneficial effects of exercise is indisputable, and the benefits of exercise far outweigh the risks in most adults. A program of regular exercise that includes cardiorespiratory, resistance, flexibility, and neuromotor exercise training beyond activities of daily living to improve and maintain physical fitness and health is essential for most adults. The ACSM recommends that most adults engage in moderate-intensity cardiorespiratory exercise training for ≥30 min·d on ≥5 d·wk for a total of ≥150 min·wk, vigorous-intensity cardiorespiratory exercise training for ≥20 min·d on ≥3 d·wk (≥75 min·wk), or a combination of moderate- and vigorous-intensity exercise to achieve a total energy expenditure of ≥500-1000 MET·min·wk. On 2-3 d·wk, adults should also perform resistance exercises for each of the major muscle groups, and neuromotor exercise involving balance, agility, and coordination. Crucial to maintaining joint range of movement, completing a series of flexibility exercises for each the major muscle-tendon groups (a total of 60 s per exercise) on ≥2 d·wk is recommended. The exercise program should be modified according to an individual's habitual physical activity, physical function, health status, exercise responses, and stated goals. Adults who are unable or unwilling to meet the exercise targets outlined here still can benefit from engaging in amounts of exercise less than recommended. In addition to exercising regularly, there are health benefits in concurrently reducing total time engaged in sedentary pursuits and also by interspersing frequent, short bouts of standing and physical activity between periods of sedentary activity, even in physically active adults. Behaviorally based exercise interventions, the use of behavior change strategies, supervision by an experienced fitness instructor, and exercise that is pleasant and enjoyable can improve adoption and adherence to prescribed exercise programs. Educating adults about and screening for signs and symptoms of CHD and gradual progression of exercise intensity and volume may reduce the risks of exercise. Consultations with a medical professional and diagnostic exercise testing for CHD are useful when clinically indicated but are not recommended for universal screening to enhance the safety of exercise.

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Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise

The primary purpose of this narrative review was to evaluate the current literature and to provide further insight into the role physical inactivity plays in the development of chronic disease and premature death. We confirm that there is irrefutable evidence of the effectiveness of regular physical activity in the primary and secondary prevention of several chronic diseases (e.g., cardiovascular disease, diabetes, cancer, hypertension, obesity, depression and osteoporosis) and premature death. We also reveal that the current Health Canada physical activity guidelines are sufficient to elicit health benefits, especially in previously sedentary people. There appears to be a linear relation between physical activity and health status, such that a further increase in physical activity and fitness will lead to additional improvements in health status.

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Health benefits of physical activity: the evidence

The purpose was to: 1) perform a systematic review of studies examining the relation between physical activity, fitness, and health in school-aged children and youth, and 2) make recommendations based on the findings. The systematic review was limited to 7 health indicators: high blood cholesterol, high blood pressure, the metabolic syndrome, obesity, low bone density, depression, and injuries. Literature searches were conducted using predefined keywords in 6 key databases. A total of 11,088 potential papers were identified. The abstracts and full-text articles of potentially relevant papers were screened to determine eligibility. Data was abstracted for 113 outcomes from the 86 eligible papers. The evidence was graded for each health outcome using established criteria based on the quantity and quality of studies and strength of effect. The volume, intensity, and type of physical activity were considered. Physical activity was associated with numerous health benefits. The dose-response relations observed in observational studies indicate that the more physical activity, the greater the health benefit. Results from experimental studies indicate that even modest amounts of physical activity can have health benefits in high-risk youngsters (e.g., obese). To achieve substantive health benefits, the physical activity should be of at least a moderate intensity. Vigorous intensity activities may provide even greater benefit. Aerobic-based activities had the greatest health benefit, other than for bone health, in which case high-impact weight bearing activities were required. The following recommendations were made: 1) Children and youth 5-17 years of age should accumulate an average of at least 60 minutes per day and up to several hours of at least moderate intensity physical activity. Some of the health benefits can be achieved through an average of 30 minutes per day. [Level 2, Grade A]. 2) More vigorous intensity activities should be incorporated or added when possible, including activities that strengthen muscle and bone [Level 3, Grade B]. 3) Aerobic activities should make up the majority of the physical activity. Muscle and bone strengthening activities should be incorporated on at least 3 days of the week [Level 2, Grade A].

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Systematic review of the health benefits of physical activity and fitness in school-aged children and youth

This 10-year follow-up evaluated the effect of physical activity and calcium intake on proximal femur bone mass (BMC) and structural indices (CSA and Z) and physical performance. A cohort of 133 premenopausal and 134 postmenopausal women with contrasting levels of physical activity (high [PA+]) and low [PA−]) and calcium intake (high [Ca+] and low [Ca−]) was measured with DXA at baseline and 5 and 10 years thereafter. Among premenopausal women, the mean (95% CI) femoral neck BMC was 3.8% (−0.1 to 7.8%) and the trochanter BMC 6.7% (2.4 to 11.3%) greater in the PA+ group than the PA− group. There was no difference between the Ca-intake groups. Among postmenopausal women, the mean femoral neck BMC was 4.2% (−0.2 to 8.8%) greater in the Ca+ group than in the Ca− group and 6.9% (2.2 to11.8%) greater in the PA+ group than in the PA− group. For trochanter BMC, the corresponding differences were 2.7% (−1.6 to 7.2%) and 5.5% (0.9 to 10.3%). The mean differences in CSA and Z were 3.8% (−0.9 to 8.7%) and 4.4% (−2.1 to 11.4%) in favor of the Ca+ group and 6.8% (1.9 to 12.0%) and 9.6% (2.5 to 17.1%) in favor of the PA+ group, respectively. Proximal femur BMC declined generally, but the initial differences between the physical activity and the calcium intake groups were maintained. High calcium intake seemed to slow the decline in trochanter BMC in premenopausal women, while high physical activity was beneficial for proximal femur, particularly among older women.

Influence of Calcium Intake and Physical Activity on Proximal Femur Bone Mass and Structure Among Pre- and Postmenopausal Women. A 10-Year Prospective Study

To the Editor: Traumatic brain injury (TBI) is a major cause of hospitalization, disability, and death worldwide, and among older adults, falling is the most common cause of TBI.1 We reported that the number and incidence of adults aged 80 years or older admitted to the hospital due to fall-induced TBI in Finland increased from 1970 through 1999.2 We now report follow-up of this population through 2011.

https://jamanetwork.com/journals/jama/articlepdf/1685851/jlt130003_1891_1892.pdf

Incidence of fall-related traumatic brain injuries among older Finnish adults between 1970 and 2011.

Summary Introduction Humeral-shaft fractures are not uncommon osteoporotic fractures. While most of the humeral-shaft fractures can be treated conservatively, some need surgical treatment. The purpose of this study was to assess the trends of the surgical treatment of humeral-shaft fractures. The study determined whether surgical treatment of humeral-shaft fractures has changed in Finland between 1987 and 2009. We assessed the number and incidence of surgically treated humeral-shaft fractures in each year and recorded the type of surgery used. Patients and methods The study covered the entire adult (>18 years) population in Finland over the 23-year period from 1 January 1987 to 31 December 2009. Data on surgically treated humeral-shaft fractures were obtained from the nationwide National Hospital Discharge Registry. Results During the 23-year study period, a total of 4469 surgical operations of the humeral shaft were performed in Finland. The male patients were markedly younger (49 years) than their female counterparts (63 years). The incidence of surgical treatment nearly doubled in men and over tripled in women. Between 1987 and 2009, there occurred a clear shift towards plating in the surgical treatment of humeral-shaft fractures. Conclusions A marked increase in the surgical treatment of humeral-shaft fractures was seen in Finland in 1987–2009. Fracture plating increased during the first decade of the millennium. Since high-quality evidence for treatment of humeral-shaft fractures is absent, critical evaluation of the chosen treatment options is needed.

Surgical treatment of humeral-shaft fractures: a register-based study in Finland between 1987 and 2009.

This prospective study investigated the incidence and pattern of acute time-loss injuries in young female and male basketball players. Eight basketball teams (n=201; mean age 14.85±1.5) participated in the follow-up study (2011-2014). The coaches recorded player participation in practices and games on a team diary. A study physician contacted the teams once a week to check new injuries and interviewed the injured players. In total, 158 injuries occurred. The overall rate of injury (per 1000 hours) was 2.64 (95% CI 2.23-3.05). Injury rate was 34.47 (95% CI 26.59-42.34) in basketball games and 1.51 (95% CI 1.19-1.82) in team practices. Incidence rate ratio (IRR) between game and practice was 22.87 (95% CI 16.71-31.29). Seventy-eight percent of the injuries affected the lower limbs. The ankle (48%) and knee (15%) were the most commonly injured body sites. The majority of injuries involved joint or ligaments (67%). Twenty-three percent of the injuries were severe causing more than 28 days absence from sports. Number of recurrent injuries was high (28% of all injuries), and most of them were ankle sprains (35 of 44, 79%). No significant differences were found in injury rates between females and males during games (IRR 0.88, 0.55, to 1.40) and practices (IRR 1.06, 0.69, to 1.62). In conclusion, ankle and knee ligament injuries were the most common injuries in this study. Moreover, the rate of recurrent ankle sprains was alarming.

High ankle injury rate in adolescent basketball: A 3-year prospective follow-up study.

Dual-energy x-ray absorptiometry (DXA) is a precise and effective method for measuring bone mineral density (BMD) and content (BMC) at various skeletal sites in the human, but its precision for measuring low BMD and BMC in tiny rat bones has scarcely been evaluated. The short-term precision of DXA (Norland XR-26) for eight regions of interest (ROI) was determined by measuring dissected, not totally defleshed hindlimbs from four rats of differently weights 10 times consecutively. The accuracy of the BMD (area) measurement was also evaluated. The following average precision values (coefficients of variation) with negligible reanalysis error were obtained for BMD and BMC measurements: 0.7 and 1.2% (total); 0.9 and 1.2% (femur); 1.3 and 2.8% (tibia); 1.3 and 2.1% (foot); 2.1 and 4.7% (proximal femur); 1.4 and 2.9% (femoral shaft); 1.8 and 5.6% (distal femur); and 2.7 and 7.6% (proximal tibia). As for the accuracy, BMD measured in tiny bones is likely to be markedly underestimated. We conclude that the standard DXA technique without additional modification for small animal measurements is a precise method for BMD and BMC measurements at multiple sites in rat hindlimb in vitro.

Pekka Kannus

Papers

Influence of Calcium Intake and Physical Activity on Proximal Femur Bone Mass and Structure Among Pre- and Postmenopausal Women. A 10-Year Prospective Study

Incidence of fall-related traumatic brain injuries among older Finnish adults between 1970 and 2011.

Surgical treatment of humeral-shaft fractures: a register-based study in Finland between 1987 and 2009.

High ankle injury rate in adolescent basketball: A 3-year prospective follow-up study.

Precision of measurement by dual-energy X-ray absorptiometry of bone mineral density and content in rat hindlimb in vitro