The Effects of Exercising Muscle Mass on Post Exercise Hypotension
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Journal of Human Hypertension (2000) 14, 317–320 2000 Macmillan Publishers Ltd All rights reserved 0950-9240/00 $15.00 www.nature.com/jhh ORIGINAL ARTICLE The effects of exercising muscle mass on post exercise hypotension JR MacDonald, JD MacDougall and CD Hogben Departments of Kinesiology and Medicine, McMaster University, Hamilton, Ontario L8S 4K1, Canada Nine recreationally active, borderline hypertensive sub- the effect to be prolonged following the leg exercise. We jects completed 30 min of arm ergometry (ARM) at 65% conclude that the mass of the working muscle does not V˙ O2 peak and 30 min of leg ergometry (LEG) at 70% directly effect the magnitude of post-exercise hypoten- V˙ O2 Peak (randomised order). Blood pressure was moni- sion (PEH) but may influence the duration of the tored before and for 1 h after exercise using the Fin- response. These results suggest that a central mech- apres method. Systolic, diastolic and mean blood press- anism or decreased vascular responsiveness is respon- ures were significantly reduced for the entire 1 h post sible for PEH. exercise. This reduction was independent of exercise Journal of Human Hypertension (2000) 14, 317–320 modality, but there was an indication for the duration of Keywords: blood pressure; ergometry; Finapres Introduction Subjects and methods The mechanism(s) responsible for post-exercise Subjects hypotension (PEH) has not been established. Studies Nine recreationally active participants (seven males, examining both peripherally1–3 and centrally4–7 two females), with borderline hypertension (five mediated mechanisms have produced inconsistent screening measurements of 135 Ͼ systolic blood results. pressure Ͻ 150 and/or 85 Ͼ diastolic blood pressure At the same relative percentage of limb-specific Ͻ 95 mm Hg) volunteered to participate in this ˙ VO2 Peak, arm and leg ergometry are known to elicit study. Subjects had a mean age of 23 ± 4 (mean ± similar blood pressure and heart rate responses.8 It s.d.) years, a mean height of 176 ± 13 cm and a mean has been estimated that the mass of the upper limbs weight of 77.4 ± 7.5 kg. Average body mass index account for approximately 7.6% of the body’s mass, was similar between the males (24.74) and females whereas the lower limbs account for approximately (24.67) and listed within the ‘healthy range’.10 The 32%.9 Thus at the same relative exercise intensity, McMaster University Human Ethics Committee the total active muscle mass and absolute metabolic approved the study and subjects were advised of the rate would be greater for leg ergometry than for arm risks before providing written informed consent. ergometry. It also follows that while intramuscular concentration of metabolites and ions (eg, adenosine and K+) would be similar for the two modes of exer- Preliminary testing cise, the absolute production of these vasodilator The Finapres system was used to measure blood substances and release into the circulation would be pressure in this study. We have recently discussed greatest with leg ergomety. Therefore, one might the accuracy of the resting Finapres measures fol- hypothesise that if PEH is mediated by some periph- lowing exercise (see MacDonald et al).11 On five sep- eral factor, leg ergometry would be expected to arate days, participants were required to undergo result in a greater decline in blood pressure. It was resting Finapres blood pressure measurement after felt that by examining the influence of the exercising a seated period of 20–30 min. The five systolic and muscle mass, some insight may be provided as to five diastolic blood pressures were averaged and 1 the mechanism responsible for PEH. standard deviation (s.d.) was calculated. If, during one of the experimental trials, initial resting press- ure (either systolic or diastolic) was not within 1 s.d. of the subject’s pre-trial average, the test was termin- ated and rescheduled for another day. Prior to beginning the study, limb-specific maxi- mal oxygen uptake was determined using incremen- Correspondence: Jay R MacDonald, Departments of Kinesiology tal arm and leg ergometry tests to exhaustion. Both and Medical Sciences, Ivor Wynne Centre, McMaster University, Hamilton, Ontario L8S 4K1, Canada tests used an electrically braked cycle/arm erg- Received 20 August 1999; revised 30 November 1999; accepted ometer (Eric Jaeger, Hoechberg, Germany). During 28 December 1999 each test, subjects exercised at a cadence greater Muscle mass and hypotension JR MacDonald et al 318 than 60 revolutions per min (rpm). At the com- form and the lowest point in the waveform prior to pletion of each 2-min interval, the power output was the last inflection point, respectively. Mean arterial increased by 20–60 Watts, dependent on the limbs pressure (MAP) was determined by the quotient of used and state of fatigue. Volitional exhaustion was the integrated pressure and the duration of the deemed to be the point at which subjects could no time interval. longer maintain a cadence of 60 rpm. The mean of All blood pressure variables were assessed using the two consecutive highest oxygen uptake values single, two-factor, repeated measures, analyses of was considered the limb-specific V˙ O2 Peak. Expired variance (ANOVA) with trial and time of measure- gas was collected using a one-way air flow valve ment as the repeated measures. The Tukey Honestly (Hans Rudolph #2700, Hans Rudolph Inc, Kansas Significant Difference (HSD) method was used to City, MO, USA) and analysed on-line via an IBM identify the location of any significant differences. compatible computer using the TurboFit software A probability level of P р 0.05 was considered stat- package (Vacumetrics, Ventura, CA, USA) coupled istically significant. All values are expressed as with an AMETEK S3A/1 oxygen analyser (Applied mean ± s.d. unless otherwise stated. Electrochemistry, Pittsburg, PA, USA) and a Hewlett Packard 78356A carbon dioxide analyser (Hewlett Results Packard, Mississauga, ON, Canada). Both analysers were calibrated prior to and following each test The effects of exercise on post-exercise blood press- using gases of known O2 and CO2 content. ure are illustrated in Figure 1. No differences were Limb-specific V˙ O2 Peak was 30.96 mL kg min for found between ARM or LEG trials. Collectively, SBP arm exercise (ARM) and 46.81 mL kg min for leg was significantly (F(6,48) = 5.64, P Ͻ 0.01) reduced exercise (LEG). Although the original intent was to from pre-exercise values between 5 and 60 min post- have subjects perform each exercise session at 70% exercise inclusive. The pressure decrement was con- ෂ of limb-specific V˙ O2 Peak, initial trials demonstrated stant at 15 mm Hg below pre-exercise values that most subjects could only maintain arm ergome- (140 ± 12 mm Hg) for the entire post-exercise moni- try at 65% of V˙ O2 Peak. Therefore a revised 65% and toring. DBP was also decreased for the entire post- = Ͻ 70% of the limb-specific V˙ O2 Peak was calculated for exercise period (F(6,48) 3.28, P 0.01). The nadir the ARM and LEG trials respectively as the target of DBP occurred at 45 min post exercise (82 ± 13 vs oxygen consumption during the submaximal exer- 73 ± 11), and collectively fluctuated no more than 3 cise trials. mm Hg during the post-exercise period. Subjects refrained from exercising during the 24 h MAP also remained below pre-exercise values for prior to testing and consumed no stimulants or the entire hour post exercise (F(6,48) = 3.70, P Ͻ depressants known to affect blood pressure (eg, caf- feine and alcohol). Protocol After a 4 h fast, the subjects reported to the labora- tory and remained quietly seated for 30 min. They then underwent resting Finapres blood pressure measurements verified by auscultation. The Fina- pres transducer was placed at mid-sternal level and coupled to an on-line data acquisition package (Windaq/200, DataQ Instruments Inc, Akron, OH, USA) sampling at a frequency of 300 Hz. Calibration of the Finapres was completed using an internal calibration sequence as well as a mercury man- ometer. The transducer was calibrated to show a lin- ear response between 0 and 300 mm Hg. On separate days, subjects were required to perform 30 min of arm ergometry at a power output that elicited 65% of arm V˙ O2 Peak, and 30 min of leg ergometry at a power output that elicited 70% of leg V˙ O2 Peak (randomised order). Finapres blood pressure was monitored continu- ously throughout the session with 2-min windows recorded at rest, 5, 10, 15, 30, 45 and 60 min post- exercise for subsequent analysis. Analysis Blood pressure waveforms were analysed using the Windaq data analysis software (DataQ Instruments Figure 1 The effects of 30 min of arm and leg exercise on post Inc). Systolic (SBP) and diastolic (DBP) blood press- exercise blood pressure (mean ± s.e.m.). *Indicates pooled data ure were calculated as the highest point in the wave- is significantly different from baseline. Post, min post exercise. Journal of Human Hypertension Muscle mass and hypotension JR MacDonald et al 319 seated rest.1 We are therefore confident that the dec- rements in blood pressure documented here are a result of the exercise interventions. This study indi- cates that the magnitude of the decrement in post- exercise blood pressure is not influenced by the mass of the working muscle. This would lend sup- port to two theories of post-exercise hypotension. Firstly, PEH may be mediated by factors originat- ing in the brain and cardiovascular control centres. Rodent work has suggested that the central opioid and serotonergic systems, leading to changes in sympathetic activity may be the source of PEH.6,7,12 However, studies examining these systems in humans are contradictory4,5 and have not been pur- sued in recent years.