Central and peripheral hemodynamics during maximal leg extension exercise

Making the case for resistance training in improving vascular function and skeletal muscle capillarization

Through decades of empirical data, it has become evident that resistance training (RT) can improve strength/power and skeletal muscle hypertrophy. Yet, until recently, vascular outcomes have historically been underemphasized in RT studies, which is underscored by several exercise-related reviews supporting the benefits of endurance training on vascular measures. Several lines of evidence suggest large artery diameter and blood flow velocity increase after a single bout of resistance exercise, and these events are mediated by vasoactive substances released from endothelial cells and myofibers (e.g., nitric oxide). Weeks to months of RT can also improve basal limb blood flow and arterial diameter while lowering blood pressure. Although several older investigations suggested RT reduces skeletal muscle capillary density, this is likely due to most of these studies being cross-sectional in nature. Critically, newer evidence from longitudinal studies contradicts these findings, and a growing body of mechanistic rodent and human data suggest skeletal muscle capillarity is related to mechanical overload-induced skeletal muscle hypertrophy. In this review, we will discuss methods used by our laboratories and others to assess large artery size/function and skeletal muscle capillary characteristics. Next, we will discuss data by our groups and others examining large artery and capillary responses to a single bout of resistance exercise and chronic RT paradigms. Finally, we will discuss RT-induced mechanisms associated with acute and chronic vascular outcomes.

High-intensity resistance exercise is not as effective as traditional high-intensity interval exercise for increasing the cardiorespiratory response and energy expenditure in recreationally active subjects

PURPOSE

Traditional high-intensity interval exercise (HIIE) highly stimulates the cardiorespiratory system and increases energy expenditure (EE) during exercise. High-intensity resistance exercise (HIRE) has become more popular in recreationally active subjects. The physiological responses to HIRE performed with light or moderate load is currently largely unknown. Here, we examined the effect of the type of interval exercise [HIRE at 40% (HIRE40) and 60% (HIRE60) 1-RM vs. traditional HIIE] on the cardiorespiratory response and EE during and after exercise.

METHODS

Fifteen recreationally active adults randomly completed traditional HIIE on an ergocyle, HIRE40 and HIRE60. The sessions consisted of two sets of ten 30-s intervals (power at 100% VO_2max during HIIE; maximal number of repetitions for 10 different free-weight exercises during HIRE40 and HIRE60) separated by 30-s active recovery periods. Gas exchange, heart rate (HR) and EE were assessed during and after exercise.

RESULTS

VO_2mean, VO_2peak, HR_mean, the time spent above 90% VO_2max and HR_max, and aerobic EE were lower in both HIRE sessions compared with HIIE (P < 0.05). Anaerobic glycolytic contribution to total exercise EE was higher in HIRE40 and HIRE60 compared with HIIE (P < 0.001). EE from excess post-exercise oxygen consumption (EPOC) was similar after the three sessions. Overall, similar cardiorespiratory responses and EE were found in HIRE40 and HIRE60.

CONCLUSIONS

HIRE is not as effective as HIIE for increasing the cardiorespiratory response and EE during exercise, while EPOC remains similar in HIRE and HIIE. These parameters are not substantially different between HIRE40 and HIRE60.

The effect of an acute bout of resistance exercise on carotid artery strain and strain rate

Arterial wall mechanics likely play an integral role in arterial responses to acute physiological stress. Therefore, this study aimed to determine the impact of low and moderate intensity double‐leg press exercise on common carotid artery (CCA) wall mechanics using 2D vascular strain imaging. Short‐axis CCA ultrasound images were collected in 15 healthy men (age: 21 ± 3 years; stature: 176.5 ± 6.2 cm; body mass; 80.6 ± 15.3 kg) before, during, and immediately after short‐duration isometric double‐leg press exercise at 30% and 60% of participants' one‐repetition maximum (1RM: 317 ± 72 kg). Images were analyzed for peak circumferential strain (PCS), peak systolic and diastolic strain rate (S‐SR and D‐SR), and arterial diameter. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP) were simultaneously assessed and arterial stiffness indices were calculated post hoc. A two‐way repeated measures ANOVA revealed that during isometric contraction, PCS and S‐SR decreased significantly (P < 0.01) before increasing significantly above resting levels post exercise (P < 0.05 and P < 0.01, respectively). Conversely, D‐SR was unaltered throughout the protocol (P = 0.25). No significant differences were observed between the 30% and 60% 1RM trials. Multiple regression analysis highlighted that HR, BP, and arterial diameter did not fully explain the total variance in PCS, S‐SR, and D‐SR. Acute double‐leg press exercise is therefore associated with similar transient changes in CCA wall mechanics at low and moderate intensities. CCA wall mechanics likely provide additional insight into localized intrinsic vascular wall properties beyond current measures of arterial stiffness.

Hemodynamic and hormonal responses to a short-term low-intensity resistance exercise with the reduction of muscle blood flow

We investigated the hemodynamic and hormonal responses to a short-term low-intensity resistance exercise (STLIRE) with the reduction of muscle blood flow. Eleven untrained men performed bilateral leg extension exercise under the reduction of muscle blood flow of the proximal end of both legs pressure-applied by a specially designed belt (a banding pressure of 1.3 times higher than resting systolic blood pressure, 160-180 mmHg), named as Kaatsu. The intensity of STLIRE was 20% of one repetition maximum. The subjects performed 30 repetitions, and after a 20-seconds rest, they performed three sets again until exhaustion. The superficial femoral arterial blood flow and hemodynamic parameters were measured by using the ultrasound and impedance cardiography. Serum concentrations of growth hormone (GH), vascular endothelial growth factor (VEGF), noradrenaline (NE), insulin-like growth factor (IGF)-1, ghrelin, and lactate were also measured. Under the conditions with Kaatsu, the arterial flow was reduced to about 30% of the control. STLIRE with Kaatsu significantly increased GH (0.11+/-0.03 to 8.6+/-1.1 ng/ml, P < 0.01), IGF-1 (210+/-40 to 236+/-56 ng/ml, P < 0.01), and VEGF (41+/-13 to 103+/-38 pg/ml, P < 0.05). The increase in GH was related to neither NE nor lactate, but the increase in VEGF was related to that in lactate (r = 0.57, P < 0.05). Ghrelin did not change during the exercise. The maximal heart rate (HR) and blood pressure (BP) in STLIRE with Kaatsu were higher than that without Kaatsu. Stroke volume (SV) was lower due to the decrease of the venous return by Kaatsu, but, total peripheral resistance (TPR) did not change significantly. These results suggest that STLIRE with Kaatsu significantly stimulates the exercise-induced GH, IGF, and VEGF responses with the reduction of cardiac preload during exercise, which may become a unique method for rehabilitation in patients with cardiovascular diseases.

Musculoskeletal fitness, health outcomes and quality of life

The health benefits and quality-of-life outcomes of a fit musculoskeletal system (musculoskeletal fitness) are reviewed in this article. The World Health Organization suggests health is a state of complete physical, mental or social well-being and not merely the absence of disease or infirmity. Physical health includes such characteristics as body size and shape, sensory acuity, susceptibility to disease and disorders, body functioning, recuperative ability and the ability to perform certain tasks. One aspect of physical health is the musculoskeletal system, which consists of 3 components; muscular strength, endurance and flexibility. Muscular strength (dynamic) is defined as the maximum force a muscle or muscle group can generate at a specific velocity. Muscular endurance is the ability of a muscle or muscle group to perform repeated contractions against a load for an extended period of time. Flexibility has 2 components, dynamic or static, where dynamic flexibility is the opposition or resistance of a joint to motion, that is, the forces opposing movement rather than the range of movement itself. Static flexibility is the range of motion about ajoint, typically measured as the degree of arc at the end of joint movement. If strength, endurance and flexibility are not maintained, musculoskeletal fitness is then compromised which can significantly impact physical health and well-being. Many health benefits are associated with musculoskeletal fitness, such as reduced coronary risk factors, increased bone mineral density (reduced risk of osteoporosis), increased flexibility, improved glucose tolerance, and greater success in completion of activities of daily living (ADL). With aging, the performance of daily tasks can become a challenge. Additionally, falls, bone fractures and the need for institutional care indicate a musculoskeletal weakness as we age. The earlier in life an individual becomes physically active the greater the increase in positive health benefits; however, becoming physically active at any age will benefit overall health. Improved musculoskeletal fitness (for example, through resistance training combined with stretching) is associated with an enhanced health status. Thus, maintaining musculoskeletal fitness can increase overall quality of life.

Cardiovascular stress associated with concentric and eccentric isokinetic exercise in young and older adults

Heart rate (HR), mean arterial blood pressure (MAP), and rate-pressure product (RPP) responses to submaximal isokinetic concentric (CON) and eccentric (ECC) knee extension exercise were compared at the same absolute torque output in 20 young (mean+/-SD=23.2+/-1.7 years) and 20 older (mean+/-SD=75.2+/-4.6 years) adults. After determination of peak CON and ECC torques, subjects performed separate, randomly ordered, 2-minute bouts of isokinetic CON and ECC exercise (90 degrees/s, exercise intensity: 50% of CON peak torque). CON exercise elicited greater changes in HR, MAP, and RPP than ECC exercise (p<.001) for both age groups. There were no age-related differences in HR, MAP, or RPP responses for either CON or ECC exercise. At the same absolute torque output, isokinetic CON knee extension exercise elicited significantly greater increases in cardiovascular stress than ECC exercise in both young and older adults. This result has implications for determining appropriate fitness and rehabilitation programs.

Acute responses to resistance training and safety

Resistance training is widely used in fitness programs for healthy individuals of all ages and has become accepted as part of the exercise rehabilitation process for patients with coronary artery disease. It is only during the past decade that the acute circulatory responses to resistance exercise have been investigated directly, using intra-arterial measurement techniques and two-dimensional echocardiography. This review examines the factors that influence the acute circulatory responses to resistance training. These include the number of repetitions, the absolute and relative load, the muscle mass engaged in the lifting, the joint angle, and the Valsalva maneuver. There is discussion of the responses in patients with coronary artery disease and the effects of resistance training on the acute responses. The review ends with a discussion of the safety of this form of exercise and concludes that it is safe and appropriate for most healthy individuals and many of those with different diseases.

Ventilatory response to positive and negative work in patients with chronic obstructive pulmonary disease

In healthy subjects, oxygen consumption and cardiorespiratory responses are lower during eccentric exercise (negative work, Wneg) than during concentric exercise (positive work, Wpos) at the same work load. The aim of the present study was to investigate the ventilatory response to Wneg in patients with chronic obstructive pulmonary disease (COPD). The study population consisted of 12 subjects with COPD [forced expiratory volume in 1 s (FEV1) mean (SD): 1.5 (0.4) 1, 46 (16)% of predicted]. Concentric and eccentric exercise tests (6 min exercise; interval > or = 1 h) were performed in random order at constant work loads of 25 and 50% of the individual maximal (positive) work capacity. Expired ventilation per minute (VE), oxygen consumption (VO2) and carbon dioxide production (VCO2) were 30% lower during Wneg than during Wpos for both work intensities. The breathing reserve during 25% Wneg was 11 (8)% and during 50% Wneg was 18 (14)% higher than during Wpos at corresponding work loads (P < 0.01). VE/VO2 and VE/VCO2 were similar during Wpos and Wneg. Arterial carbon dioxide tension (PaCO2) increased by 0.1 (0.4) kPa during 50% Wneg and by 0.7 (0.5) kPa during 50% Wpos (P < 0.01). During 50% Wneg' perceived leg effort (modified Borg scale) tended to be higher than perceived breathlessness (2.4 (1.2) vs. 2.0 (1.1). It was concluded that in subjects with COPD, the ventilatory requirements of Wneg were considerably lower than those of Wpos at similar work loads up to 50% of maximal work capacity. During Wneg, the ventilatory reserve was higher and gas exchange was less disturbed as a result of a lower VO2 and VCO2.

Effects of active recovery on power output during repeated maximal sprint cycling

The effects of active recovery on metabolic and cardiorespiratory responses and power output were examined during repeated sprints. Male subjects (n = 13) performed two maximal 30-s cycle ergometer sprints, 4 min apart, on two separate occasions with either an active [cycling at 40 (1)% of maximal oxygen uptake; mean (SEM)] or passive recovery. Active recovery resulted in a significantly higher mean power output (W) during sprint 2, compared with passive recovery [W] 603 (17) W and 589 (15) W, P < 0.05]. This improvement was totally attributed to a 3.1 (1.0)% higher power generation during the initial 10 s of sprint 2 following the active recovery (P < 0.05), since power output during the last 20 s sprint 2 was the same after both recoveries. Despite the higher power output during sprint 2 after active recovery, no differences were observed between conditions in venous blood lactate and pH, but peak plasma ammonia was significantly higher in the active recovery condition [205 (23) vs 170 (20) mumol .l-1; P < 0.05]. No differences were found between active and passive recovery in terms of changes in plasma volume or arterial blood pressure throughout the test. However, heart rate between the two 30-s sprints and oxygen uptake during the second sprint were higher for the active compared with passive recovery [148 (3) vs 130 (4) beats.min-1; P < 0.01) and 3.3 (0.1) vs 2.8 (0.1) l.min-1; P < 0.01]. These data suggest that recovery of power output during repeated sprint exercise is enhanced when low-intensity exercise is performed between sprints. The beneficial effects of an active recovery are possibly mediated by an increased blood flow to the previously exercised muscle.

Dissociated oxygen uptake response to an incremental intermittent repetitive lifting and lowering exercise in humans

Five subjects performed a maximal exercise test of repetitive lifting and lowering, with a discontinuous protocol of incremental exercise (3 min) and relative rest (2 min). Exercise periods consisted of repetitive lifting and repetitive lifting and lowering at increasing movement frequencies. Relative rest periods consisted of ergometer cycling at a constant, low power output. An unexpected, dissociated, response of cardiovascular and pulmonary parameters was found: during relative rest, values for oxygen uptake, carbon dioxide production, pulmonary ventilation and tidal volume were significantly higher than during the preceding exercise periods, though exercise intensity was much lower. To our knowledge, such a response has not been reported in previous studies. Since the response could not be attributed to methodological or technical factors, it is hypothesized that the type of exercise itself impeded the optimal performance of the oxygen transporting system. The function of the pulmonary system could have been influenced by a high intra-abdominal pressure, the involvement of respiratory muscles in stabilizing trunk and head, a flexed trunk posture and the entrainment of respiratory frequency with movement frequency. More likely, the function of the cardiovascular system was hindered by a high blood pressure and high intramuscular pressures. Since this response occurred at low exercise intensities, optimal functioning of the cardiovascular and pulmonary system during daily activities of repetitive lifting and lowering could similarly be impeded. The hypotheses put forward could also explain the lower peak oxygen uptake reported during repetitive lifting, compared to running and cycling.

Cardiodynamic responses during seated and supine recovery from supramaximal exercise

The cardiodynamic responses of 9 healthy men (mean age +/- SD, 22.3 +/- 2.0 yrs) were measured during seated and supine passive recovery following the Wingate Anaerobic Power Test (WAPT). Stroke index (SI) was determined noninvasively using impedance cardiographic techniques. During the initial stages of seated recovery, SI progressively increased (1 min, 60.4 +/- 6.6 ml/m2; 3 min, 64.6 +/- 5.9 ml/m2) and achieved peak levels by 5 min (70.5 +/- 6.2 ml/m2). Between Minutes 3 and 10 of seated recovery, SI was significantly (p < or = 0.05) higher than the preexercise value (46.0 +/- 4.0 ml/m2). A similar response pattern for SI was observed during supine recovery. The systemic vascular resistance index (SVRI) decreased by 101% and 114% from preexercise baseline values after 1 min of recovery in the supine and seated postures, respectively. The persistent rise in SI during the first 10 min of passive seated recovery may be explained by the sustained attenuation in SVRI coupled with the anticipated residual myocardial inotropic effects following the WAPT.

Application of impedance cardiography during exercise

Impedance cardiography has been used over the last 30 years to measure stroke volume on a beat-by-beat basis. Cardiac output has been successfully measured with either upper or lower body exercise during light or moderate workloads. With strenuous exercise, movement artifacts severely limit the acquisition of a quality impedance cardiogram. Advances in computer technology and signal conditioning techniques have created the next generation of impedance cardiograph systems. The purpose of this study was to evaluate such a system, the noninvasive continuous cardiac output monitor (NCCOM3-R7), at rest and during submaximal upright cycle exercise. In addition, the relationships between thoracic impedance (Z(o)), first derivative of the change in thoracic impedance (dZ/dt) and posture were evaluated using the NCCOM3-R7 and the Minnesota impedance cardiograph 304B (MIC). Twenty-eight healthy men and women participated. The Z(o) progressively increased when moving from the supine to seated to standing position with both instruments. However, the NCCOM3-R7 yielded lower Z(o) values and higher dZ/dt values compared with the MIC for all postures. Z(o) and dZ/dt values appear to be dependent upon factors such as posture, gender, electrical current, and characteristics of the instrumentation. Exercise cardiac output values seemed reasonable for most subjects, although population subsets exist where the accuracy must be questioned. The general consensus supported by the impedance literature and reaffirmed by the present observations is that impedance cardiography provides a reasonable estimate of the directional changes in stroke volume and cardiac output during exercise and can be used to monitor changes in thoracic fluid balance. As this technology evolves and is further refined, it will undoubtedly play an increasing role in environmental medicine, exercise stress testing, cardiac rehabilitation, and sports medicine.

Effect of breathing techniques on blood pressure response to resistance exercise

Twenty novice male weight lifters performed resistance exercises using three different breathing techniques to determine the effects on blood pressure. Systolic and diastolic blood pressures were measured by an automated non-invasive method while subjects performed the single arm curl and double knee extension using the different breathing techniques. Performing the Valsalva manoeuvre (breath-holding) during either the single arm curl or double knee extension produced the highest blood pressure responses. Inhaling during the concentric phase of the exercise was associated with blood pressure elevations that were similar to the elevations observed with exhaling during the concentric phase. The heart rate response was slightly higher with inhalation. These results suggest that performing the Valsalva manoeuvre exaggerates the blood pressure response to resistance exercise. In addition, coupling inhalation with the concentric phase of the lift offers no cardiovascular advantage over coupling exhalation with the concentric phase of the lift.