Assistant Professor of Exercise Science, Elon University
Osteoporosis is a disease state typified by a low bone mass which increases the risk of fracture. Statistics suggest that around 1 in 3 women and 1 in 5 men over 50 years old will suffer from low bone mass in their lifetime, with hundreds of millions worldwide currently afflicted. During growth there is a key period where an individual's bone is being laid down most rapidly and improving bone development during this time has been shown to have lasting impacts for Osteoporosis prevention later in life. Numerous avenues have been explored in search of ways to improve bone development with physical activity and structured exercise being some of the most promising. That said, my research examines not only the benefits of loading bone via physical activity during growth but also the potential detrimental effects of 'not loading' bone through excess sedentary behavior. Sedentary behavior is broadly defined as any activity with a low energy expenditure, typically in a seated or lying posture and this type of behavior is synonymous with our convenience driven society. Some have compared the effects of sedentary behavior to space flight where astronauts struggle to load their skeletons due to a lack of gravity, leading to a drastically compromised skeletal health upon return to earth. Though much of the focus of physical activity research has looked at the effects of 'inactivity' or not getting enough activity throughout the day, this concept is wholly separate from sedentary behavior. An individual could be both sedentary and active at the same time, for example, a 13 year old gymnast trains daily at her gym but once she gets home (and throughout the day at school) she does no other activity, just laying around on social media and watching Netflix. This girl would likely meet the public recommendations for daily physical activity (60 minutes per day of moderate-to-vigorous physical activity) but would also spend a substantial proportion of her day being sedentary. In the context of bone health, we know that the mechanical stimulus that occurs when we load our bones during activity is key to the development of strong, healthy bones. However, my research aims to define whether the potential detrimental effects of unloading during excess sedentary behavior prevent today's youth from optimally developing their bones, increasing their risk of Osteoporosis later in life.
Abstract: Sedentary behaviours, defined as non exercising seated activities, have been shown to have deleterious effects on health. It has been hypothesised that too much sitting time can have a detrimental effect on bone health in youth. The aim of this study is to test this hypothesis by exploring the association between objectively measured volume and patterns of time spent in sedentary behaviours, time spent in specific screen-based sedentary pursuits and bone mineral content (BMC) accrual in youth.NHANES 2005-2006 cycle data includes BMC of the femoral and spinal region via dual-energy X-ray absorptiometry (DEXA), assessment of physical activity and sedentary behaviour patterns through accelerometry, self reported time spent in screen based pursuits (watching TV and using a computer), and frequency of vigorous playtime and strengthening activities. Multiple regression analysis, stratified by gender was performed on N = 671 males and N = 677 females aged from 8 to 22 years.Time spent in screen-based sedentary behaviours is negatively associated with femoral BMC (males and females) and spinal BMC (females only) after correction for time spent in moderate and vigorous activity. Regression coefficients indicate that an additional hour per day of screen-based sitting corresponds to a difference of -0.77 g femoral BMC in females [95% CI: -1.31 to -0.22] and of -0.45 g femoral BMC in males [95% CI: -0.83 to -0.06]. This association is attenuated when self-reported engagement in regular (average 5 times per week) strengthening exercise (for males) and vigorous playing (for both males and females) is taken into account. Total sitting time and non screen-based sitting do not appear to have a negative association with BMC, whereas screen based sedentary time does. Patterns of intermittence between periods of sitting and moderate to vigorous activity appears to be positively associated with bone health when activity is clustered in time and inter-spaced with long continuous bouts of sitting.Some specific sedentary pursuits (screen-based) are negatively associated with bone health in youth. This association is specific to gender and anatomical area. This relationship between screen-based time and bone health is independent of the total amount of physical activity measured objectively, but not independent of self-reported frequency of strengthening and vigorous play activities. The data clearly suggests that the frequency, rather than the volume, of osteogenic activities is important in counteracting the effect of sedentary behaviour on bone health. The pattern of intermittence between sedentary periods and activity also plays a role in bone accrual, with clustered short bouts of activity interspaced with long periods of sedentary behaviours appearing to be more beneficial than activities more evenly spread in time.
Pub.: 08 Jan '14, Pinned: 06 Jul '17
Abstract: Today's youths spend close to 60% of their waking hours in sedentary activities; however, we know little about the potentially deleterious effects of sedentary time on bone health during this key period of growth and development. Thus, our objective was to determine whether sedentary time is associated with bone architecture, mineral density, and strength in children, adolescents, and young adults.We used high-resolution peripheral quantitative computed tomography (Scanco Medical) to measure bone architecture (trabecular and cortical microstructure and bone macrostructure) and cortical and total bone mineral density (BMD) at the distal tibia (8% site) in 154 males and 174 females (9-20 yr) who were participants in the University of British Columbia Healthy Bones III study. We applied finite element analysis to high-resolution peripheral quantitative computed tomography scans to estimate bone strength. We assessed self-reported screen time in all participants using a questionnaire and sedentary time (volume and patterns) in a subsample of participants with valid accelerometry data (89 males and 117 females; ActiGraph GT1M). We fit sex-specific univariate multivariable regression models, controlling for muscle cross-sectional area, limb length, maturity, ethnicity, dietary calcium, and physical activity.We did not observe independent effect of screen time on bone architecture, BMD, or strength in either sex (P > 0.05). Likewise, when adjusted for muscle cross-sectional area, limb length, maturity, ethnicity, dietary calcium, and physical activity, accelerometry-derived volume of sedentary time and breaks in bouts of sedentary time were not a determinant of bone architecture, BMD, or strength in either sex (P > 0.05).Further study is warranted to determine whether the lack of association between sedentary time and bone architecture, BMD, and strength at the distal tibia is also present at other skeletal sites.
Pub.: 02 Jul '14, Pinned: 06 Jul '17
Abstract: Bone strength is influenced by bone geometry, density, and bone microarchitecture, which adapt to increased mechanical loads during growth. Physical activity (PA) is essential for optimal bone strength accrual; however, less is known about how sedentary time influences bone strength and its determinants. Thus, our aim was to investigate the prospective associations between PA, sedentary time, and bone strength and its determinants during adolescence. We used HR-pQCT at distal tibia (8% site) and radius (7% site) in 173 girls and 136 boys (aged 9 to 20 years at baseline). We conducted a maximum of four annual measurements at the tibia (n = 785 observations) and radius (n = 582 observations). We assessed moderate-to-vigorous PA (MVPA) and sedentary time with accelerometers (ActiGraph GT1M). We aligned participants on maturity (years from age at peak height velocity) and fit a mixed-effects model adjusting for maturity, sex, ethnicity, leg muscle power, lean mass, limb length, dietary calcium, and MVPA in sedentary time models. MVPA was a positive independent predictor of bone strength (failure load [F.Load]) and bone volume fraction (BV/TV) at the tibia and radius, total area (Tt.Ar) and cortical porosity (Ct.Po) at the tibia, and negative predictor of load-to-strength ratio at the radius. Sedentary time was a negative independent predictor of Tt.Ar at both sites and Ct.Po at the tibia and a positive predictor of cortical thickness (Ct.Th), trabecular thickness (Tb.Th), and cortical bone mineral density (Ct.BMD) at the tibia. Bone parameters demonstrated maturity-specific associations with MVPA and sedentary time, whereby associations were strongest during early and mid-puberty. Our findings support the importance of PA for bone strength accrual and its determinants across adolescent growth and provide new evidence of a detrimental association of sedentary time with bone geometry but positive associations with microarchitecture. This study highlights maturity-specific relationships of bone strength and its determinants with loading and unloading. Future studies should evaluate the dose-response relationship and whether associations persist into adulthood. © 2017 American Society for Bone and Mineral Research.
Pub.: 23 Mar '17, Pinned: 06 Jul '17
Abstract: The purpose of the study was to examine the effects of sprint interval training (SIT) and moderate-intensity continuous cycle training (MICT), with equal estimated energy expenditure during training on body composition and aerobic capacity. Body composition measured via dual-energy X-ray absorptiometry and aerobic capacity were assessed following 6 weeks of training in previously inactive overweight/obese young women (n = 52; age, 20.4 ± 1.5 years; body mass index, 30.3 ± 4.5 kg·m(-2), 67.3% white). Training was performed in a group-exercise format that mimicked cycling classes offered by commercial fitness facilities, and included 3 weekly sessions of either 30-s "all-out" sprints followed by 4 min of active recovery (SIT), or continuous cycling at 60%-70% heart rate reserve to expend a similar amount of energy. Participants were randomized to SIT or MICT, attended a similar number of sessions (15.0 ± 1.5 sessions vs. 15.8 ± 1.9 sessions, P = 0.097) and expended a similar amount of energy (541.8 ± 104.6 kJ·session(-1) vs. 553.5 ± 138.1 kJ·session(-1), P = 0.250). Without significant changes in body mass (P > 0.05), greater relative reductions occurred in SIT than in MICT in total fat mass (3.6% ± 5.6% vs. 0.6% ± 3.9%, P = 0.007), and android fat mass (6.6% ± 6.9% vs. 0.7% ± 6.5%, P = 0.002). Aerobic capacity (mL·kg(-1)·min(-1)) increased significantly following both interventions (P < 0.05), but the relative increase was 2-fold greater in SIT than in MICT (14.09% ± 10.31% vs. 7.06% ± 7.81%, P < 0.001). In conclusion, sprint-interval cycling reduces adiposity and increases aerobic capacity more than continuous moderate-intensity cycling of equal estimated energy expenditure in overweight/obese young women.
Pub.: 04 Nov '16, Pinned: 06 Jul '17
Abstract: Endurance athletes commonly ingest caffeine as a means to enhance training intensity and competitive performance. A widely-used source of caffeine is coffee, however conflicting evidence exists regarding the efficacy of coffee in improving endurance performance. In this context, the aims of this evidence-based review were three-fold: 1) to evaluate the effects of pre-exercise coffee on endurance performance, 2) to evaluate the effects of coffee on perceived exertion during endurance performance, and 3) to translate the research into usable information for athletes to make an informed decision regarding the intake of caffeine via coffee as a potential ergogenic aid. Searches of three major databases were performed using terms caffeine, and coffee, or coffee-caffeine, and endurance, or aerobic. Included studies (n=9) evaluated the effects of caffeinated coffee on human subjects, provided the caffeine dose administered, administered caffeine ≥45 minutes before testing, and included a measure of endurance performance (e.g., time trial). Significant improvements in endurance performance were observed in five of nine studies, which were on average 24.2% over controls for time to exhaustion trials, and 3.1% for time to completion trials. Three of six studies found that coffee reduced perceived exertion during performance measures significantly more than control conditions (p<0.05). Based on the reviewed studies there is moderate evidence supporting the use of coffee as an ergogenic aid to improve performance in endurance cycling and running. Coffee providing 3-8.1mg/kg (1.36-3.68mg/lb) of caffeine may be used as a safe alternative to anhydrous caffeine to improve endurance performance.
Pub.: 17 Nov '15, Pinned: 06 Jul '17
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