Diabetes Publish Ahead of Print, published online November 14, 2007 The role of free‐living daily walking in human weight‐gain and obesity James A. Levine*, Shelly K. McCrady, Lorraine M. Lanningham‐Foster, Paul H. Kane, Randal C. Foster, Chinmay U. Manohar. Endocrine Research Unit, Mayo Clinic, Rochester, MN, 55905. USA. Running title: Obesity and walking *Corresponding Author Received for publication 17 June 2007 and accepted in revised form 4 November 2007. Additional information for this article can be found in an online appendix at http://diabetes.diabetesjournals.org. Copyright American Diabetes Association, Inc., 2007 Obesity and walking ABSTRACT Objective: Diminished daily physical activity explains, in part, why obesity and diabetes have become worldwide epidemics. In particular, chair‐use has replaced ambulation so that obese individuals tend to sit for ~2 ½ hours/day more than lean counterparts. Here we address the hypotheses that free‐living daily walking distance is decreased in obesity compared to lean subjects and second, experimental weight precipitates decreased daily walking. Research Design and Methods: During weight‐maintenance feeding, we measured free‐living walking using a validated system that captures locomotion and body movement for ten days in 22 healthy lean and obese sedentary individuals. These measurements were then repeated after the lean and obese subjects were overfed by 1000 kcal/day for eight weeks. Results: We found that free‐living walking is comprised of many (~47), short duration (<15 minutes), low velocity (~1 mph) walking bouts. Lean subjects walked 3 ½ miles/day more than obese subjects (n=10, 10.3 + 2.5 versus n=12, 6.7 + 1.8 miles/day; P=0.0009). With overfeeding, walking distance decreased by 1 ½ miles/day compared to baseline values (‐1.5 + 1.7 miles/day; p=0.0005). The decrease in walking that accompanied overfeeding occurred to a similar degree in the lean (‐1.4 + 1.9 miles/day; p=0.04) and obese (‐1.6 + 1.7 miles/day; p=0.008) subjects. Conclusions: Walking is decreased in obesity and declines with weight gain. This may represent a continuum whereby progressive increases in weight are associated with progressive decreases in walking distance. By identifying walking as pivotal in weight gain & obesity we hope to add credence to a future that is ambulatory. KEY WORDS. obesity, physical activity, weight gain, walking 2 Obesity and walking besity is epidemic in address the hypothesis that weight developed countries and is gain is associated with a decrease in O emerging in middle‐ and even walking distance, we compared free‐ low‐income countries; this in part living walking before and after explains the unprecedented increase overfeeding. in Type 2 Diabetes world‐wide (1). It is widely agreed that this partially SUBJECTS AND METHODS reflects mounting sedentariness (2; 3). Subjects. Twenty two healthy, At the beginning of the twentieth sedentary volunteers were recruited century 90% of worldʹs population aged (mean + SD) 39 + 8 years. Ten was rural. However, over the last subjects (5 females and 5 males) were century, more than two billion lean (BMI<25 kg/m2) and 12 subjects (7 agriculturalists have become city females and 5 males) were obese (BMI dwellers (4). In the latter transition, >29 kg/m2)(Table 1). All the subjects physical activity has declined (5). In worked in sedentary jobs, 19 were particular chair‐use has replaced white, 2 black and 1 Hispanic and the ambulation (6) so that obese majority of the subjects were middle individuals tend to sit for ~2 ½ socioeconomic class and lived within hours/day more than lean 10 miles of the laboratory. None of counterparts (7). Walking is the the subjects worked in our principal component of non‐exercise laboratories or on the study team. activity thermogenesis (NEAT) which Subjects were excluded if they used is the energy expenditure association any medication at the time of the with free‐living daily activities (8; 9). study or within six months of prior to This is because people walk for the study, exercised more than twice several hours each day and, even at each week, smoked, used alcohol, slow velocity, walking doubles energy were pregnant, had any acute or expenditure (10); hence the product of chronic illness, complained of joint the time engaged in walking and its problems or pain, failed psychological energetic equivalent is numerically evaluation for depression & eating substantial. We therefore wondered disorder, reported mental illness or whether walking might be had unsteady body weight (>2 kg mechanistically important in weight‐ fluctuation over the six months prior gain and obesity. To address the to study). hypothesis that free‐living daily Study design. The subjects were walking distance is decreased in studied as outpatients for 11 weeks. obesity we examined the Meals were prepared in the metabolic characteristics of free‐living walking kitchen at the Mayo Clinic General in lean and obese people. Then, to Clinical Research Center (GCRC). All 3 Obesity and walking foods were weighed to within 1g. For Dual X‐ray Absorptiometry (DXA) the first three weeks volunteers were (Lunar, Madison, WI) after the three fed to establish the dietary intake weeks of baseline feeding and after necessary to maintain steady‐state the eight weeks of overfeeding. The body weight. The diet composition test‐retest difference for duplicate was 45 % carbohydrate, 35 % fat and measurements of fat mass were <2 %. 20 % protein. Subjects were instructed Measurement of daily body posture not to adopt new exercise practices and movement. We used a validated and to continue their usual daily physical activity monitoring system activities and occupation. For the last (PAMS) that captures data on body eight weeks of the study subjects posture and movement in duplicate received a 1000 kcal/day above their continuously every half‐second for 10 weight‐maintenance needs. For the consecutive days (7; 11‐13). PAMS last 10 days of weight maintenance comprises six sensors (Figure 1), four feeding and for the last 10 days inclinometers (each of which captures overfeeding, subjects wore a Physical two axes of acceleration against the Activity Monitoring System (PAMS‐ earth’s gravitational field, CXTA02, described below) to characterize the Crossbow Technology Inc., San Jose, duration and number and intensity of CA) and two triaxial accelerometers the bouts of walking and to measure (each captures motion in x, y and z other body postures and movements. axes, CXL02LF3‐R, Crossbow When the study was complete, all Technology Inc). The 14 axes of data subjects were assisted, as needed, to were binned and stored every half‐ lose any excess weight that had been second on two data loggers (Ready gained. Informed written consent was DAQ AD2000, Crossbow Technology obtained after the nature and possible Inc). The inclinometers were attached consequences of the study were to the right and left outer aspect of the explained and the study was trunk and right and left outer aspect approved by the Mayo IRB. of the thigh. The two accelerometers Measurements of body composition. were placed over the base of the spine. The volunteer’s body weight was Specially designed underwear (Figure measured each morning under 1) was used to attach the sensors. The standardized conditions (with an two data loggers were stored in a empty bladder, without shoes and pouch worn around the waist. The wearing consistent, light clothing). PAMS weighed <1kg. Every 24 hours, These measures were performed by study staff removed the sensors while trained GCRC personnel using the the subject showered for 15 minutes. same calibrated scale (ScaleTronix During this time, data from the data 5005; S/N 5‐1700, Wheaton, IL). Body loggers were downloaded to a fat was measured in duplicate using personal computer and analyzed 4 Obesity and walking using Matlab scripts (Mathworks). day the posture sensors for the thighs The time taken showering was taken and chest and, the back to represent ‘standing’ for this period accelerometers were aligned. Three of time. The accelerometers were postures were thereby defined: calibrated for walking velocity daily • If the chest posture sensors and and the inclinometers were validated the thigh posture sensors for accuracy and precision daily both indicated horizontal – the using an electronic bench‐testing person was lying down. protocol and while each subject • If the chest posture sensors walked on a calibrated treadmill at 1, indicated vertical and the thigh 2 and 3 mph each for 2 minutes. posture sensors indicated horizontal – the person was Sensor determination of body posture sitting down. using PAMS was correct for 700/700 • If the chest posture sensors measurements of posture compared to indicated vertical and the thigh written responses by two observers posture sensors indicated and for the 440 daily tests. There were vertical – the person was log linear relationships between standing or walking. accelerometer output and velocity How was standing distinguished from with r2>0.98 in all cases. The walking? The two triaxial relationship between the paired accelerometers on the back record accelerometers showed an Intraclass data on body movement. The Correlation Coefficient (ICC) of 0.99. principal acceleration with walking is We have reported previously that in the vertical axis as a person elevates factorial determinations of NEAT their body weight against gravity (the from PAMS showed a linear positive z axis). However, if someone is relationship with total NEAT walking forwards, there is also calculated from doubly labeled water acceleration in the forward‐backward (corrected ICC=0.90, P<0.001)(7) and axis. Thus when a person with room calorimeter measurements rhythmically elevates and descends (12; 13). This approach was validated during walking, the z axis defines using a room calorimeter (12) and walking easily. This can be doubly labeled water (7; 14). independently confirmed by the fact Data analysis and statistics.