Eur J Appl Physiol DOI 10.1007/s00421-015-3171-3
ORIGINAL ARTICLE
Role of obesity on cerebral hemodynamics and cardiorespiratory responses in healthy men during repetitive incremental lifting Lora A. Cavuoto1 · Rammohan V. Maikala2
Received: 24 November 2014 / Accepted: 7 April 2015 © Springer-Verlag Berlin Heidelberg 2015
Abstract Purpose The goal of this study was to quantify obesityrelated differences in systemic physiologic responses and cerebral hemodynamics during physical work to exhaustion. Methods Twenty men, ten who are obese and ten of healthy weight, completed an incremental exercise lifting a box from 25 cm below to 25 cm above knuckle height at 10 lifts/min. The lifting started with a load of 5 kg and was increased by 2 kg every 2 min until participants reached either voluntary fatigue or two of the American College of Sports Medicine endpoints for maximum aerobic capacity. Cardiorespiratory and prefrontal hemodynamic responses were measured simultaneously during rest, incremental lifting, and recovery. Results The non-obese group lifted for ~64 % longer than the obese group. Both groups reached similar peak pulmonary oxygen uptake at the termination of exercise; however, when these responses were expressed relative to their body mass, the obese group had ~60 % reduced oxygen uptake. As the load increased, steady increases in cerebral oxygenation and blood volume responses were observed in both groups up to ~90 % of the lifting trial. In contrast, at higher intensities (near 100 % of the lifting trial), cerebral oxygenation and blood volume decreased in the obese group,
whereas it plateaued or slightly increased in the non-obese group, with greatest cerebral oxygen extraction occurring at the cessation of lifting trial. Conclusion These findings suggest that acute exposure to repetitive lifting exercise decreases cardiorespiratory responses and cerebral hemodynamics in the group who are obese, which may contribute to their reduced lifting capacity. Keywords Aerobic capacity · Body mass index · Fatigue · Incremental exercise · Near-infrared spectroscopy Abbreviations ACSM American College of Sports Medicine BMI Body mass index Hb Hemoglobin HHb Deoxygenated hemoglobin NIRS Near-infrared spectroscopy O2Hb Oxygenated hemoglobin PetCO2 End tidal partial pressure of carbon dioxide RPE Rating of perceived exertion tBV Total blood volume TOI Tissue oxygenation index
Introduction Communicated by William J. Kraemer. * Lora A. Cavuoto [email protected] 1
Department of Industrial and Systems Engineering, University at Buffalo, 324 Bell Hall, Buffalo, NY 14260, USA
2
Providence Strategic and Management Services, Providence Regional Medical Center, Everett, WA 98201, USA
Over two-thirds of the US adult population is either overweight or obese [defined as having a body mass index (BMI) >25 kg/m2], and the prevalence of obesity (BMI > 30 kg/m2) has more than doubled over the past 30 years (Ogden et al. 2007). Obesity-related differences, for example, in physiological responses may negatively influence cardiovascular health, resulting in increased mortality risk (Lavie et al. 2014). At the cardiovascular level,
13
although inconclusive, obesity results in higher oxygen consumption at equivalent intensities during incremental cycling (Salvadori et al. 1992, 1999), while others reported similar maximum intensities and peak oxygen consumption between obese and non-obese individuals during cycling and knee extension (Lazzer et al. 2013; Salvadori et al. 1992, 1999). In contrast, a few authors found an obesityrelated reduction in peak intensity during cycling as well (Lazzer et al. 2013; Ofir et al. 2007). At the musculoskeletal level, obesity has been associated with a decrease in capillary density and lower blood flow to skeletal muscle (Kern et al. 1999), thereby limiting the supply of oxygen and energy sources. Further, these physiological changes may explain the reported inverse relationship between BMI and endurance time during isometric grip contractions (Eksioglu 2011), although stimulation-induced fatigue was unaffected by obesity (e.g., Maffiuletti et al. 2007). In addition, assessment of fatigue and endurance in obese populations has been limited to localized muscle fatigue during specific isometric and isokinetic tasks (Cavuoto and Nussbaum 2013a, 2014; Maffiuletti et al. 2013). At the cerebral level, initial evidence using advanced brain imaging methods shows an inverse correlation between BMI and prefrontal cortex metabolic activity, which suggests reduced brain blood flow in overweight individuals (Volkow et al. 2009; Willeumier et al. 2011). In addition, reductions in prefrontal cortex oxygenation [measured by near-infrared spectroscopy (NIRS)] have been associated with reduced muscle force-generating capacity (Bhambhani et al. 2007; Rasmussen et al. 2007). During moderate levels of exercise, cerebral oxygenation increases to accommodate the increased demand; however, at very high intensities a drop in blood flow has been observed, particularly for untrained participants (Rooks et al. 2010). Such a drop in cerebral hemodynamic responses may affect maximal work capacity and volitional fatigue (Rupp and Perrey 2008). Based on NIRS-derived cerebral hemodynamic responses from individuals with chronic fatigue syndrome, Neary et al. (2008) suggested that reduced blood flow to the brain may alter neuronal function and perception of effort. Although these cerebral tissue-related studies highlight the importance of measuring hemodynamic response in understanding the process of neurovascular coupling (i.e., neuronal activation coupled with an adequate increase in cerebral blood flow), none of the above listed studies addressed the role of central and peripheral factors on fatigue in individuals who are obese as well as fatigue differences induced by physically demanding tasks. Of concern in the workplace are the increased rates of obesity-related musculoskeletal injuries (Schmier et al. 2006), particularly as obesity is associated with a 25 % increase in the odds of a workplace injury compared to
13
Eur J Appl Physiol
non-obese workers (Lin et al. 2013). Across the entire worker population, manual materials handling such as repetitive lifting remains a common occupational task and also a major risk factor for cumulative disorders of the low back, the most common injury site (BLS 2013; Dempsey 2003). Repetitive lifting is a combination of positive (work generated by shortening of muscles) and negative (stretching of active muscles) mechanical work. Positive work is generated in raising the load to the specific destination, while both types of work are active in raising and lowering the lifter’s own body mass. With obesity, however, the added body mass of obesity alters biomechanical loading of the low back during lifting (Corbeil et al. 2013). Considering the fact that lifting-related activities are performed continuously in an 8-h shift, classification of either work capacity or worker’s abilities based on the maximal or peak aerobic capacity may facilitate in understanding fatigue over an 8-h working day and increased susceptibility to injury (Bilzon et al. 2002; McConnell et al. 1984; Waters et al. 1993a). For example, Anderson (2010) evaluated newhire delivery drivers over a two-year tenure and predicted that a unit increase in aerobic capacity results in a 3.7 % decrease in injury rate and 1.1 % decrease in termination from their work. The author also reported an approximate seven-fold ratio of predicted injury rates for the least fit group as compared to the group of most fit delivery drivers. In addition to serving as an indicator of cardiovascular fitness, maximal or peak aerobic capacity is a good predictor of the ability to perform work safely without overexertion or discomfort (Hammermeister et al. 2001; Maikala and Bhambhani 2006). Although a plethora of literature have addressed the implications of repetitive lifting to fatigue and injuries at the workplace, in majority, these studies examined the role of the musculoskeletal system (e.g., Yang et al. 2007, 2011) and cardiorespiratory responses (e.g., Kell and Bhambhani 2003; Nindl et al. 1997; Commissaris and Toussaint 1996) on job performance during a variety of lifting-related protocols for different population groups with and without back pain (Kell and Bhambhani 2003, 2006). However, none of these studies demonstrated if this lifting exercise poses either any risk to cerebral health or if the brain is a limiting factor to lifting performance. Furthermore, to date there are no studies that have simulated workplace scenarios to examine the influence of physiological fitness on repetitive lifting performance for individuals who are obese. Therefore, the goal of this study was to quantify obesity-related differences in systemic physiologic responses and cerebral hemodynamics during physical work to exhaustion. Highlighting these differences will enable the improved characterization of the effects of obesity on work capacity and task performance. It was hypothesized that the obesity would adversely affect physiological responses,
Eur J Appl Physiol Table 1 Summary of participants’ descriptive data in mean (standard deviation) Variable Age (years) Height (m) Mass (kg)* Body mass index (kg/m2)* Body adiposity indexa,* Waist circumference (cm)* Hip circumference (cm)* Skinfold thickness (mm) Chest* Abdominal* Thigh* Predicted body fat (%)b,* Trunk extension strength (Nm)c
Non-obese
any signs of elevated blood pressure, breathing difficulty, excessive sweating, or physical discomfort during cycling.
Obese
27.2 (5.1) 1.76 (0.07) 69.9 (7.0) 22.6 (1.5) 21.9 (2.5) 81.9 (6.6) 93.5 (4.4)
29.7 (4.4) 1.75 (0.05) 105.3 (11.5) 34.2 (2.5) 30.9 (1.9) 110.8 (11.0) 113.4 (5.6)
7.9 (5.4) 12.3 (7.6) 10.1 (6.2) 9.3 (5.1)
18.8 (4.4) 31.3 (5.3) 27.7 (20.8) 21.9 (5.6)
276.8 (67.5)
300.9 (62.1)
* p
ORIGINAL ARTICLE
Role of obesity on cerebral hemodynamics and cardiorespiratory responses in healthy men during repetitive incremental lifting Lora A. Cavuoto1 · Rammohan V. Maikala2
Received: 24 November 2014 / Accepted: 7 April 2015 © Springer-Verlag Berlin Heidelberg 2015
Abstract Purpose The goal of this study was to quantify obesityrelated differences in systemic physiologic responses and cerebral hemodynamics during physical work to exhaustion. Methods Twenty men, ten who are obese and ten of healthy weight, completed an incremental exercise lifting a box from 25 cm below to 25 cm above knuckle height at 10 lifts/min. The lifting started with a load of 5 kg and was increased by 2 kg every 2 min until participants reached either voluntary fatigue or two of the American College of Sports Medicine endpoints for maximum aerobic capacity. Cardiorespiratory and prefrontal hemodynamic responses were measured simultaneously during rest, incremental lifting, and recovery. Results The non-obese group lifted for ~64 % longer than the obese group. Both groups reached similar peak pulmonary oxygen uptake at the termination of exercise; however, when these responses were expressed relative to their body mass, the obese group had ~60 % reduced oxygen uptake. As the load increased, steady increases in cerebral oxygenation and blood volume responses were observed in both groups up to ~90 % of the lifting trial. In contrast, at higher intensities (near 100 % of the lifting trial), cerebral oxygenation and blood volume decreased in the obese group,
whereas it plateaued or slightly increased in the non-obese group, with greatest cerebral oxygen extraction occurring at the cessation of lifting trial. Conclusion These findings suggest that acute exposure to repetitive lifting exercise decreases cardiorespiratory responses and cerebral hemodynamics in the group who are obese, which may contribute to their reduced lifting capacity. Keywords Aerobic capacity · Body mass index · Fatigue · Incremental exercise · Near-infrared spectroscopy Abbreviations ACSM American College of Sports Medicine BMI Body mass index Hb Hemoglobin HHb Deoxygenated hemoglobin NIRS Near-infrared spectroscopy O2Hb Oxygenated hemoglobin PetCO2 End tidal partial pressure of carbon dioxide RPE Rating of perceived exertion tBV Total blood volume TOI Tissue oxygenation index
Introduction Communicated by William J. Kraemer. * Lora A. Cavuoto [email protected] 1
Department of Industrial and Systems Engineering, University at Buffalo, 324 Bell Hall, Buffalo, NY 14260, USA
2
Providence Strategic and Management Services, Providence Regional Medical Center, Everett, WA 98201, USA
Over two-thirds of the US adult population is either overweight or obese [defined as having a body mass index (BMI) >25 kg/m2], and the prevalence of obesity (BMI > 30 kg/m2) has more than doubled over the past 30 years (Ogden et al. 2007). Obesity-related differences, for example, in physiological responses may negatively influence cardiovascular health, resulting in increased mortality risk (Lavie et al. 2014). At the cardiovascular level,
13
although inconclusive, obesity results in higher oxygen consumption at equivalent intensities during incremental cycling (Salvadori et al. 1992, 1999), while others reported similar maximum intensities and peak oxygen consumption between obese and non-obese individuals during cycling and knee extension (Lazzer et al. 2013; Salvadori et al. 1992, 1999). In contrast, a few authors found an obesityrelated reduction in peak intensity during cycling as well (Lazzer et al. 2013; Ofir et al. 2007). At the musculoskeletal level, obesity has been associated with a decrease in capillary density and lower blood flow to skeletal muscle (Kern et al. 1999), thereby limiting the supply of oxygen and energy sources. Further, these physiological changes may explain the reported inverse relationship between BMI and endurance time during isometric grip contractions (Eksioglu 2011), although stimulation-induced fatigue was unaffected by obesity (e.g., Maffiuletti et al. 2007). In addition, assessment of fatigue and endurance in obese populations has been limited to localized muscle fatigue during specific isometric and isokinetic tasks (Cavuoto and Nussbaum 2013a, 2014; Maffiuletti et al. 2013). At the cerebral level, initial evidence using advanced brain imaging methods shows an inverse correlation between BMI and prefrontal cortex metabolic activity, which suggests reduced brain blood flow in overweight individuals (Volkow et al. 2009; Willeumier et al. 2011). In addition, reductions in prefrontal cortex oxygenation [measured by near-infrared spectroscopy (NIRS)] have been associated with reduced muscle force-generating capacity (Bhambhani et al. 2007; Rasmussen et al. 2007). During moderate levels of exercise, cerebral oxygenation increases to accommodate the increased demand; however, at very high intensities a drop in blood flow has been observed, particularly for untrained participants (Rooks et al. 2010). Such a drop in cerebral hemodynamic responses may affect maximal work capacity and volitional fatigue (Rupp and Perrey 2008). Based on NIRS-derived cerebral hemodynamic responses from individuals with chronic fatigue syndrome, Neary et al. (2008) suggested that reduced blood flow to the brain may alter neuronal function and perception of effort. Although these cerebral tissue-related studies highlight the importance of measuring hemodynamic response in understanding the process of neurovascular coupling (i.e., neuronal activation coupled with an adequate increase in cerebral blood flow), none of the above listed studies addressed the role of central and peripheral factors on fatigue in individuals who are obese as well as fatigue differences induced by physically demanding tasks. Of concern in the workplace are the increased rates of obesity-related musculoskeletal injuries (Schmier et al. 2006), particularly as obesity is associated with a 25 % increase in the odds of a workplace injury compared to
13
Eur J Appl Physiol
non-obese workers (Lin et al. 2013). Across the entire worker population, manual materials handling such as repetitive lifting remains a common occupational task and also a major risk factor for cumulative disorders of the low back, the most common injury site (BLS 2013; Dempsey 2003). Repetitive lifting is a combination of positive (work generated by shortening of muscles) and negative (stretching of active muscles) mechanical work. Positive work is generated in raising the load to the specific destination, while both types of work are active in raising and lowering the lifter’s own body mass. With obesity, however, the added body mass of obesity alters biomechanical loading of the low back during lifting (Corbeil et al. 2013). Considering the fact that lifting-related activities are performed continuously in an 8-h shift, classification of either work capacity or worker’s abilities based on the maximal or peak aerobic capacity may facilitate in understanding fatigue over an 8-h working day and increased susceptibility to injury (Bilzon et al. 2002; McConnell et al. 1984; Waters et al. 1993a). For example, Anderson (2010) evaluated newhire delivery drivers over a two-year tenure and predicted that a unit increase in aerobic capacity results in a 3.7 % decrease in injury rate and 1.1 % decrease in termination from their work. The author also reported an approximate seven-fold ratio of predicted injury rates for the least fit group as compared to the group of most fit delivery drivers. In addition to serving as an indicator of cardiovascular fitness, maximal or peak aerobic capacity is a good predictor of the ability to perform work safely without overexertion or discomfort (Hammermeister et al. 2001; Maikala and Bhambhani 2006). Although a plethora of literature have addressed the implications of repetitive lifting to fatigue and injuries at the workplace, in majority, these studies examined the role of the musculoskeletal system (e.g., Yang et al. 2007, 2011) and cardiorespiratory responses (e.g., Kell and Bhambhani 2003; Nindl et al. 1997; Commissaris and Toussaint 1996) on job performance during a variety of lifting-related protocols for different population groups with and without back pain (Kell and Bhambhani 2003, 2006). However, none of these studies demonstrated if this lifting exercise poses either any risk to cerebral health or if the brain is a limiting factor to lifting performance. Furthermore, to date there are no studies that have simulated workplace scenarios to examine the influence of physiological fitness on repetitive lifting performance for individuals who are obese. Therefore, the goal of this study was to quantify obesity-related differences in systemic physiologic responses and cerebral hemodynamics during physical work to exhaustion. Highlighting these differences will enable the improved characterization of the effects of obesity on work capacity and task performance. It was hypothesized that the obesity would adversely affect physiological responses,
Eur J Appl Physiol Table 1 Summary of participants’ descriptive data in mean (standard deviation) Variable Age (years) Height (m) Mass (kg)* Body mass index (kg/m2)* Body adiposity indexa,* Waist circumference (cm)* Hip circumference (cm)* Skinfold thickness (mm) Chest* Abdominal* Thigh* Predicted body fat (%)b,* Trunk extension strength (Nm)c
Non-obese
any signs of elevated blood pressure, breathing difficulty, excessive sweating, or physical discomfort during cycling.
Obese
27.2 (5.1) 1.76 (0.07) 69.9 (7.0) 22.6 (1.5) 21.9 (2.5) 81.9 (6.6) 93.5 (4.4)
29.7 (4.4) 1.75 (0.05) 105.3 (11.5) 34.2 (2.5) 30.9 (1.9) 110.8 (11.0) 113.4 (5.6)
7.9 (5.4) 12.3 (7.6) 10.1 (6.2) 9.3 (5.1)
18.8 (4.4) 31.3 (5.3) 27.7 (20.8) 21.9 (5.6)
276.8 (67.5)
300.9 (62.1)
* p
