Veronica K. Jamnik

Effect of alterations in blood volume on cardiac function during maximal exercise

Recently, we proposed that the higher stroke volume (SV) and cardiac output (Q) of endurance-trained (ETR) versus untrained (UTR) individuals are attributable primarily to the enhanced diastolic filling of ETR consequent to a larger blood volume (BV). To test this hypothesis, we examined the effects of manipulating BV on the cardiac function of six ETR and six UTR males. Both groups were examined in the control BV condition (BVctl), then ETR were examined immediately following a 500 mL reduction in BV (BVred) and UTR were examined immediately following a 500 mL expansion of BV (BVexp). In BVctl, compared with UTR, ETR had significantly greater BV (16%), maximal diastolic filling rate (47.4%), maximal ventricular emptying rate (24.6%), SVmax (31.6%), Qmax (29%) and VO2max (54.5%). Following BVexp in UTR, there were immediate significant increases in maximal diastolic filling rate (22.5%), SVmax (9.1%), Qmax (8.9%), and VO2max (12.7%). Following BVred in ETR there were immediate significant decreases in maximal diastolic filling rate (27%), SVmax (14.3%), Qmax (14.7%), and VO2max (7.0%). Maximal systolic emptying rate did not change significantly following BVred or BVexp. We conclude that changes in SV and Q consequent to alterations in BV are attributable primarily to changes in diastolic function, and the majority of the higher diastolic filling rate of ETR is due to their larger BV.

INDUCED HYPERVOLEMIA, CARDIAC FUNCTION, VO2MAX, AND PERFORMANCE OF ELITE CYCLISTS

OBJECTIVE To determine whether plasma volume expansion (PVexp) in elite endurance-trained (ET) cyclists, who already possess both a high blood volume (BV) and a high VO2max, leads to further enhancements in their cardiac function, VO2max, and endurance performance (time to exhaustion at 95% VO2max). METHODS Nine male ET cyclists (V02max = 68.9 +/- 0.6 (SEM) mL x kg(-1) x min(-1)) were studied employing a double blind, cross-over design; i) before PVexp, ii) after sham PVexp (Sham), iii) after restoration of normocythemia, iv) after PVexp (6% dextran), and v) upon reestablishment of normocythemia. RESULTS PVexp resulted in a 547 +/- 61 mL increase in BV (P < 0.05). Maximal cardiac output and maximal stroke volume were higher (P < 0.05) after PVexp, but the magnitude of these increases was only sufficient to counter the hemodilution effect (lowered O2 content) of PVexp, such that O2 transport, VO2max, and endurance performance remained unchanged. CONCLUSIONS Expansion of BV in elite ET cyclists, who already possess a high BV, does not improve their VO2max and endurance performance. Elite ET athletes may already be at an optimal BV, which is at or near the limits of their diastolic reserve capacity.

Exercise is associated with improved asthma control in adults

Global asthma control levels are suboptimal. The influence of regular exercise on asthma control is unclear. We assessed the effects of a 12-week supervised exercise intervention followed by 12 weeks of self-administered exercise on adults with partially controlled asthma (n = 21) and matched controls (n = 15). Assessments were conducted at baseline and week 12 for both the exercise and control group, and again at week 24 for the exercise group. There was a significant treatment effect on asthma control in the exercise group, as measured by the Asthma Control Questionnaire (ACQ), from baseline to week 12, compared with the control group. A clinically significant improvement (0.5 increase in ACQ score) was observed for asthma quality of life and ACQ in the exercise group from baseline to week 12. There was a significant improvement in aerobic fitness from baseline to week 24 in the exercise group. In conclusion, a 12-week supervised exercise intervention led to improvements in asthma control and quality of life in partially controlled asthmatics motivated to exercise. These improvements were maintained, while aerobic fitness and perceived asthma control significantly improved over an additional 12 weeks of self-administered exercise. These findings indicate that a structured exercise intervention can improve asthma control.

The role of physical activity in type 2 diabetes prevention: physiological and practical perspectives.

Abstract Lifestyle changes that include a nutritionally balanced diet and increased physical activity (PA) are effective intervention options for persons with prediabetes who want to prevent progression to type 2 diabetes mellitus. Although nutritional counseling is standard practice for patients in a clinical setting, an individualized PA prescription, including recommendations on the type, frequency, duration, and intensity, is much less likely to occur. This is surprising because lifestyle modifications including a PA program are at least as effective in diabetes prevention as any single pharmacological agent. The success of regular PA in improving glycemic control in persons with either prediabetes or type 2 diabetes likely results from adaptations that occur in several organs and tissues, including adipose, skeletal muscle, liver, and pancreas. Increased insulin sensitivity is an important link between increased PA, body composition, and metabolic health, and it is at this link where increases in PA and energy expenditure exert much of their effect on preventing metabolic disorders and improving symptoms of existing disease. In addition to improving insulin sensitivity, regular PA has several cardioprotective effects, especially for persons with metabolic dysfunction, and has been shown to elicit minimal adverse events in these populations. Effective PA prescription is contingent on an understanding of the underlying physiological adaptations and the differing responses to diverse modes and intensities of PA. This article highlights recent findings on the beneficial role of regular PA for improving and/or maintaining insulin sensitivity in persons with prediabetes. We also provide an evidence-informed prescription for the type, intensity, and duration of both resistance and aerobic PA in persons with prediabetes.

Exercise cardiac function in young through elderly endurance trained women.

PURPOSE To clarify the physiological reasons for the decline in aerobic power of endurance trained (ET) women with aging. METHODS Blood volume, VO2max, and exercise cardiac function were examined in 23 ET women; six age 20-29 yr, six age 40-45 yr, six age 49-54 yr, and five age 58-63 yr. RESULTS Blood volume was unchanged with aging. VO2max declined progressively at a rate of 0.51 mL x kg(-1) x min(-1) x yr(-1). During maximal exercise, there was an increase in total peripheral resistance (TPR) and a decrease in heart rate, stroke volume, and cardiac output with increasing age. At all ages, cardiac filling (diastole) was significantly faster than cardiac emptying (systole). Stroke volume did not plateau at a submaximal work rate but increased progressively to maximum. CONCLUSIONS The decline in VO2max with age in ET women is due to decreases in maximal heart rate, stroke volume and cardiac output, and the primary advantage in the exercise cardiac performance of ET women of all ages is diastolic rather than systolic function.

Fat oxidation rate and the exercise intensity that elicits maximal fat oxidation decreases with pubertal status in young male subjects

The range of exercise intensities that elicit high fat oxidation rates (FOR) in youth and the influence of pubertal status on peak FOR are unknown. In a longitudinal design, we compared FOR over a range of exercise intensities in a small cohort of developing prepubertal male subjects. Five boys all at Tanner stage 1 (ages 11-12 yr) and nine men (ages 20-26 yr) underwent an incremental cycle ergometry test to volitional exhaustion. FOR curves were determined from indirect calorimetry during the final 30 s of each increment. The same protocol was duplicated annually in the boys as they progressed through puberty. The peak FOR was considerably higher (P<0.05) in boys at Tanner 1 (8.6+/-1.5 mg.kg lean body mass(-1).min(-1)) (mean+/-SD) compared with men (4.2+/-1.1 mg.kg lean body mass(-1).min(-1)). FOR dropped as boys developed through puberty (Tanner 2/3 peak rate=7.6+/-0.6 mg.kg lean body mass(-1).min(-1); Tanner 4 peak rate=5.4+/-1.8 mg.kg lean body mass(-1).min(-1), main effect of Tanner stage; P<0.05) to the levels found in men (not significant). The exercise intensity that elicited peak FOR was higher in the boys at Tanner 1 [56+/-6% peak aerobic power (VO2 peak)] than in men (31+/-4% VO2 peak) (P<0.001). This value tended to decrease by Tanner stage 4 (45+/-10% VO2 peak, main effect of Tanner stage; P=0.06). We conclude that, compared with men, prepubertal boys have higher relative FOR throughout a wide range of exercise intensities and that FOR drops as boys develop through puberty.

High VO2max with no history of training is primarily due to high blood volume

PURPOSE To investigate the high VO2max observed occasionally in young men who have no history of training. METHODS VO2max, blood volume (BV), maximal stroke volume (SVmax), maximal cardiac output (Qmax), and related measurements (reported as mean +/- SEM) were studied in six men (mean age 20.0 +/- 0.5 yr) with no history of training, who all had a VO2max below 49 mL.kg-1.min-1 (LO group) and six age- and weight-matched men (mean age 19.5 +/- 0.5 yr) with no history of training, who all had a VO2max above 62.5 mL.kg-1.min-1 (HI group). RESULTS Compared with the LO group, the HI group had a higher SVmax (149 +/- 5 vs 102 +/- 5 mL), higher Qmax (28.9 +/- 0.9 vs 20.0 +/- 1.0 L.min-1) and higher BV (88.1 +/- 3.8 vs 76.7 +/- 0.9 mL.kg-1). The BV of four participants in the HI group (mean = 92.3 +/- 4.3 mL.kg-1) was substantially higher than the BV of all participants in the LO group, but two participants in the HI group had a BV (mean = 79.7 +/- 0.8 mL.kg-1) that was similar to the mean BV of the LO group. CONCLUSION The primary explanation for the high VO2max observed occasionally in young men who have no history of training is a naturally occurring (perhaps genetically determined) high BV that brings about a high SVmax and Qmax. However, some young men with no history of training have a high VO2max, SVmax, and Qmax possibly because a greater portion of their BV is hemodynamically active.

Cardiac performance in endurance-trained and moderately active young women

PURPOSE To compare the cardiac performance of endurance-trained (ET) and moderately active (MA) young women before exercise and throughout incremental work rates to maximum with particular interest in whether their stroke volume (SV) levels off at a submaximal work rate or increases to maximum. METHODS Blood volume (BV), and exercise cardiac performance were examined in seven ET (VO2max = 64.3 +/- 2.0 mL.kg(-1).min(-1)) and seven MA (VO2max = 42.1 +/- 1.0 mL.kg(-1).min(-1)) women, aged 18-30 yr. Cardiac time intervals were measured at matched heart rates (HR). RESULTS ET had a significantly larger BV than MA in both mL (ET = 5053 +/- 139, MA = 4327 +/- 202) and mL.kg(-1) (ET = 83.1 +/- 1.4, MA = 72.9 +/- 2.7). The SV of ET was significantly larger than the SV of MA throughout exercise, and the SV of ET increased progressively throughout incremental work rates to maximum. Although the SV of MA initially leveled off at a submaximal work rate, it underwent a secondary increase at very heavy work rates. Both diastolic filling rate (DFR) and left ventricular emptying rate (LVER) were significantly faster in ET compared with MA at HR of 150 bpm, 170 bpm and HRmax, and in both ET and MA, DFR was significantly faster than LVER at 170 bpm and HRmax. CONCLUSIONS In young women, ET have a larger SV than MA due to an enhanced DFR and LVER, with the primary advantage being DFR (possibly due to their larger BV). In addition, the SV of ET increases progressively throughout incremental work rates to maximum with no plateau, whereas the SV of MA levels off through moderate to heavy work rates then undergoes a secondary increase at very heavy work rates.

Evidence-based risk assessment and recommendations for physical activity clearance: Consensus Document 2011 1

The Physical Activity Readiness Questionnaire (PAR-Q) and the Physical Activity Readiness Medical Evaluation (PARmed-X) are internationally known preparticipation screening tools developed on the basis of expert opinion. The primary purposes of this consensus document were to seek evidence-based support for the PAR-Q and PARmed-X forms, to identify whether further revisions of these instruments are warranted, to determine how people responding positively to questions on the PAR-Q can be safely cleared without medical referral, and to develop exercise clearance procedures appropriate for various clinical conditions across the human lifespan. Seven systematic reviews were conducted, examining physical-activity-related risks and effective risk-stratification procedures for various prevalent chronic conditions. An additional systematic review assessed the risks associated with exercise testing and training of the general population. Two gap areas were identified and evaluated systematically: the role of the qualified exercise professional and the requisite core competencies required by those working with various chronic conditions; and the risks associated with physical activity during pregnancy. The risks associated with being physically inactive are markedly higher than transient risks during and following an acute bout of exercise in both asymptomatic and symptomatic populations across the lifespan. Further refinements of the PAR-Q and the PARmed-X (including online versions of the forms) are required to address the unique limitations imposed by various chronic health conditions, and to allow the inclusion of individuals across their entire lifespan. A probing decision-tree process is proposed to assist in risk stratification and to reduce barriers to physical activity. Qualified exercise professionals will play an essential role in this revised physical activity clearance process.

Construction, validation, and derivation of performance standards for a fitness test for correctional officer applicants

The purpose of this investigation was to develop and validate a fitness test for correctional officer (CO) applicants (FITCO) and to establish associated standards of acceptability. The FITCO incorporated the most important, physically demanding, and frequently occurring tasks of a CO. It consists of (i) a simulated cell search; (ii) an emergency response circuit (ERC), involving a 60-m run while scaling 4 sets of stairs, followed by simulations of an inmate control, wrist restraint, arm retraction, and 40-m mannequin drag; and (iii) a test of aerobic fitness. The validity of the FITCO was established by very high congruence between the oxygen consumption, heart rate, and rating of perceived exertion of incumbent COs while performing the ERC with the same measurements while COs were performing the on-the-job tasks on which the ERC was based. The content validity of the FITCO was confirmed by very high Likert ratings (>6 on a 7-point scale) by both male and female incumbent COs of all ages concerning the importance, relatedness, physical demands, and overall appropriateness of the FITCO for evaluating CO applicants. We conclude that because the forces built into the ERC and the FITCO standards were both derived from the performance of safe and efficient incumbent female COs of all ages, and both the validity and test-retest reliability (intraclass correllation coefficient = 0.977) of the FITCO are very high, the FITCO was properly constructed to meet the requirements of the Supreme Court of Canadas Meiorin Decision.