Cardiorespiratory and Autonomic Nervous System Responses to Prolonged Eccentric Cycling

Investigation of left atrial mechanical function and left ventricular systolic and diastolic parameters in athletes performing resistance exercise and combined exercise

Some individuals who go to fitness centers for various purposes perform resistance exercise (RE) alone, while others engage in combined exercise (CE) by including cardio exercises along with RE. Studying the effects of these two different training methods on left ventricular (LV) systolic and diastolic parameters and left atrial mechanical function is an important step toward understanding the effects of different types of exercise on cardiac function. This knowledge has significant implications for public health, as it can inform the development of targeted and effective exercise programs that prioritize cardiovascular health and reduce the risk of adverse outcomes. Therefore, the primary aim of this study is to comprehensively investigate the LV systolic and diastolic parameters of athletes who engage in RE and CE using ECHO, to contribute to the growing body of literature on the cardiovascular effects of different types of exercise. Forty-two amateur athletes aged between 17 and 52 were included in our study. The participants consisted of the RE (n = 26) group who did only resistance exercise during the weekly exercise period, and the CE group (n = 16) who also did cardio exercise with resistance exercises. After determining sports age (year), weekly exercise frequency (day), and training volume (min) in addition to demographic information of RE and CE groups, left ventricular systolic and diastolic parameters and left atrial functions were determined by ECHO. Findings from our study revealed that parameters including the left ventricular end-diastolic diameter (LVEDD) (p = .008), left ventricular end-diastolic volume (LVEDV) (p = .020), stroke volume index (SV-I) (p = .048), conduit volume (CV-I) (p = .001), and aortic strain (AS) (p = .017) were notably higher in the RE group compared to the CE group. Also left atrial active emptying volüme (LAAEV) of CE was higher than the RE group (p = .031). In conclusion, the cardiac parameters of the RE group showed more athlete's heart characteristics than the CE group. These results may help to optimize the cardiovascular benefits of exercise routines while minimizing the potential risks associated with improper training.

Cardiovascular Responses to Eccentric Cycling Based on Perceived Exertion Compared to Concentric Cycling, Effect of Pedaling Rate, and Sex

Interest in eccentric exercises has increased over the last decades due to its efficiency in achieving moderate-high intensity muscular work with reduced metabolic demands. However, individualizing eccentric exercises in rehabilitation contexts remains challenging, as concentric exercises mainly rely on cardiovascular parameters. To overcome this, perceived exertion could serve as an individualization tool, but the knowledge about cardiovascular responses to eccentric cycling based on perceived exertion are still scarce. For this purpose, the cardiorespiratory parameters of 26 participants were assessed during two 5 min bouts of concentric cycling at 30 and 60 rpm and two bouts of eccentric cycling at 15 and 30 rpm matched for rating of perceived exertion. With this method, we hypothesized higher exercise efficiency during eccentric cycling for a same perceived exertion. The results revealed significantly elevated heart rate and cardiac index at higher pedalling rates during concentric (p < 0.001), but not during eccentric cycling (p ≈ 1). Exercise efficiency was higher during concentric cycling (64%), decreasing with pedalling rate, while eccentric cycling exhibited increased work rates (82%), and increased by over 100% with higher pedalling rate. Hence, eccentric cycling, with lower cardiorespiratory work for the same perceived exertion, facilitates higher work rates in deconditioned populations. However, further studies are needed for effective individualization.

Acute physiological responses to eccentric cycling: a systematic review and meta-analysis

INTRODUCTION

Eccentric cycling (ECCCYC) has attracted considerable interest due to its potential applicability for exercise treatment/training of patients with poor exercise tolerance as well as healthy and trained individuals. Conversely, little is known about the acute physiological responses to this exercise modality, thus challenging its proper prescription. This study aimed to provide precise estimates of the acute physiological responses to ECCCYC in comparison to traditional concentric cycling (CONCYC).

EVIDENCE ACQUISITION

Searches were performed until November 2021 using the PubMed, Embase, and ScienceDirect databases. Studies that examined individuals' cardiorespiratory, metabolic, and perceptual responses to ECCCYC and CONCYC sessions were included. Bayesian multilevel meta-analysis models were used to estimate the population mean difference between acute physiological responses from ECCCYC and CONCYC bouts. Twenty-one studies were included in this review.

EVIDENCE SYNTHESIS

The meta-analyses showed that ECCCYC induced lower cardiorespiratory (i.e., V̇O2, V̇E, and HR), metabolic (i.e., [BLa]), and perceptual (i.e., RPE) responses than CONCYC performed at the same absolute power output, while greater cardiovascular strain (i.e., greater increases in HR, Q, MAP, [norepinephrine], and lower SV) was detected when compared to CONCYC performed at the same V̇O2.

CONCLUSIONS

The prescription of ECCCYC based on workloads used in the CONCYC sessions may be considered safe and, therefore, feasible for the rehabilitation of individuals with poor exercise tolerance. However, the prescription of ECCCYC based on the V̇O2 obtained during CONCYC sessions should be conducted with caution, especially in clinical settings, since there is a high probability of additional cardiovascular overload in this condition.

Fractal Correlation Properties of Heart Rate Variability as a Biomarker for Intensity Distribution and Training Prescription in Endurance Exercise: An Update

While established methods for determining physiologic exercise thresholds and intensity distribution such as gas exchange or lactate testing are appropriate for the laboratory setting, they are not easily obtainable for most participants. Data over the past two years has indicated that the short-term scaling exponent alpha1 of Detrended Fluctuation Analysis (DFA a1), a heart rate variability (HRV) index representing the degree of fractal correlation properties of the cardiac beat sequence, shows promise as an alternative for exercise load assessment. Unlike conventional HRV indexes, it possesses a dynamic range throughout all intensity zones and does not require prior calibration with an incremental exercise test. A DFA a1 value of 0.75, reflecting values midway between well correlated fractal patterns and uncorrelated behavior, has been shown to be associated with the aerobic threshold in elite, recreational and cardiac disease populations and termed the heart rate variability threshold (HRVT). Further loss of fractal correlation properties indicative of random beat patterns, signifying an autonomic state of unsustainability (DFA a1 of 0.5), may be associated with that of the anaerobic threshold. There is minimal bias in DFA a1 induced by common artifact correction methods at levels below 3% and negligible change in HRVT even at levels of 6%. DFA a1 has also shown value for exercise load management in situations where standard intensity targets can be skewed such as eccentric cycling. Currently, several web sites and smartphone apps have been developed to track DFA a1 in retrospect or in real-time, making field assessment of physiologic exercise thresholds and internal load assessment practical. Although of value when viewed in isolation, DFA a1 tracking in combination with non-autonomic markers such as power/pace, open intriguing possibilities regarding athlete durability, identification of endurance exercise fatigue and optimization of daily training guidance.

Analysis of Fractal Correlation Properties of Heart Rate Variability during an Initial Session of Eccentric Cycling

Eccentric cycling (ECC) has attracted attention as a method to improve muscle strength and aerobic fitness in populations unable to tolerate conventional methods. However, agreement on exercise prescription targets have been problematic. The current report is an initial exploration of a potentially useful tool, a nonlinear heart rate (HR) variability (HRV) index based on the short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA a1), which has been previously shown to correspond to exercise intensity. Eleven male volunteers performed 45 min of concentric (CON) cycling and ECC separated by 1 month. Work rates were matched for HR (~50% of the maximal HR) during the first 5 min and remained stable thereafter. HRV, HR, oxygen consumption (VO2), and cycling power were monitored and evaluated at elapsed times of 10 (T10) and 45 (T45) minutes duration. HR significantly increased between ECC T10 and ECC T45 (p = 0.003, d = 1.485), while DFA a1 significantly decreased (p = 0.004, d = 1.087). During CON, HR significantly increased (p < 0.001 d = 1.570) without significant DFA a1 change (p = 0.48, d = 0.22). Significantly higher HR was observed at T45 in ECC than in CON (p = 0.047, d = 1.059). A session of unaccustomed ECC lead to decreased values of DFA a1 at T45 in comparison to that seen with CON at similar VO2. ECC lead to altered autonomic nervous system balance as reflected by the loss of correlation properties compared to CON.

Acute and Delayed Effects of Time-Matched Very Short "All Out" Efforts in Concentric vs. Eccentric Cycling

BACKGROUND

To the authors' knowledge, there have been no studies comparing the acute responses to "all out" efforts in concentric (isoinertial) vs. eccentric (isovelocity) cycling.

METHODS

After two familiarization sessions, 12 physically active men underwent the experimental protocols consisting of a 2-min warm-up and 8 maximal efforts of 5 s, separated by 55 s of active recovery at 80 rpm, in concentric vs. eccentric cycling. Comparisons between protocols were conducted during, immediately after, and 24-h post-sessions.

RESULTS

Mechanical (Work: 82,824 ± 6350 vs. 60,602 ± 8904 J) and cardiometabolic responses (mean HR: 68.8 ± 6.6 vs. 51.3 ± 5.7% HRmax, lactate: 4.9 ± 2.1 vs. 1.8 ± 0.6 mmol/L) were larger in concentric cycling (p < 0.001). The perceptual responses to both protocols were similarly low. Immediately after concentric cycling, vertical jump was potentiated (p = 0.028). Muscle soreness (VAS; p = 0.016) and thigh circumference (p = 0.045) were slightly increased only 24-h after eccentric cycling. Serum concentrations of CK, BAG3, and MMP-13 did not change significantly post-exercise.

CONCLUSIONS

These results suggest the appropriateness of the eccentric cycling protocol used as a time-efficient (i.e., ~60 kJ in 10 min) and safe (i.e., without exercise-induced muscle damage) alternative to be used with different populations in future longitudinal interventions.

Elevated body temperature contributes to the increased heart rate response during eccentric compared to concentric cycling when matched for oxygen consumption

A cardiovascular requirement to facilitate thermal homeostasis may partly contribute to the elevated heart rate during eccentric cycling. This study compared the body temperature response to a bout of eccentric (ECC) and concentric (CON) cycling to account for the difference in heart rate. Eight (N = 8) aerobically trained males (age 35 y [SD 8], peak oxygen consumption 3.82 L.min^-1 [SD 0.79]) completed an ECC cycling trial (60% PPO) followed by an oxygen consumption/duration matched CON trial (30   ∘ C , 35% RH) on a separate day. Trial termination was determined as an elevation in aural temperature, a surrogate of deep body temperature, by +0.5   ∘ C during ECC. Mean skin (8-sites) and body temperature (weighting of 80:20 for auditory canal and mean skin temperature) were calculated. Matching the oxygen consumption between the trials increased external work during ECC cycling (CON: 71 [SD 14] ECC: 194 [SD 38] W, p < 0.05) and elevated aural temperature (+0.5   ∘ C ) by 20 min 32 s [SD 9 min 19 s] in that trial. The peak rate of rise in aural temperature was significantly greater in ECC (CON: 0.012 [SD 0.007] ECC: 0.031 [SD 0.002] ^oC.s^-1, p < 0.05). Aural, mean skin and body temperature were significantly higher during the ECC trial (p < 0.05) and this was accompanied by elevated mean heart rate (CON: 103 [SD 14] ECC: 118 [SD 12] b.min^-1, p < 0.05) and thermal discomfort (p < 0.05). Moderate load eccentric cycling imposes an elevated thermal strain when compared to concentric cycling. This requirement for dissipating heat, in part, explains the elevated heart rate during eccentric cycling.

Moving forward with backward pedaling: a review on eccentric cycling

PURPOSE

There is a profound gap in the understanding of the eccentric cycling intensity continuum, which prevents accurate exercise prescription based on desired physiological responses. This may underestimate the applicability of eccentric cycling for different training purposes. Thus, we aimed to summarize recent research findings and screen for possible new approaches in the prescription and investigation of eccentric cycling.

METHOD

A search for the most relevant and state-of-the-art literature on eccentric cycling was conducted on the PubMed database. Literature from reference lists was also included when relevant.

RESULTS

Transversal studies present comparisons between physiological responses to eccentric and concentric cycling, performed at the same absolute power output or metabolic load. Longitudinal studies evaluate responses to eccentric cycling training by comparing them with concentric cycling and resistance training outcomes. Only one study investigated maximal eccentric cycling capacity and there are no investigations on physiological thresholds and/or exercise intensity domains during eccentric cycling. No study investigated different protocols of eccentric cycling training and the chronic effects of different load configurations.

CONCLUSION

Describing physiological responses to eccentric cycling based on its maximal exercise capacity may be a better way to understand it. The available evidence indicates that clinical populations may benefit from improvements in aerobic power/capacity, exercise tolerance, strength and muscle mass, while healthy and trained individuals may require different eccentric cycling training approaches to benefit from similar improvements. There is limited evidence regarding the mechanisms of acute physiological and chronic adaptive responses to eccentric cycling.

Leg Muscle Activity and Perception of Effort before and after Four Short Sessions of Submaximal Eccentric Cycling

Background: This study tested muscle activity (EMG) and perception of effort in eccentric (ECC) and concentric (CON) cycling before and after four sessions of both. Methods: Twelve volunteers naïve to ECC cycling attended the laboratory six times. On day 1, they performed a CON cycling peak power output (PPO) test. They then carried-out four sessions comprising two sets of 1 to 1.5-min cycling bouts at 5 intensities (30, 45, 60, 75, and 90% PPO) in ECC and CON cycling. On day 2 and day 6 (two weeks apart), EMG root mean square of the vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), and soleus (SOL) muscles, was averaged from 15 to 30 s within each 1-min bout and perception of effort was asked after 45 s. Results: Before the four cycling sessions, while VL EMG was lower in ECC than CON cycling, most variables were not different. Afterwards, ECC cycling exhibited lower RF EMG at 75 and 90% PPO (all p < 0.02), lower VL and BF EMG at all exercise intensities (all p < 0.02), and inferior SOL EMG (all p < 0.04) except at 45% PPO (p = 0.07). Perception of effort was lower in ECC cycling at all exercise intensities (all p < 0.03) but 60% PPO (p = 0.11). Conclusions: After four short sessions of ECC cycling, the activity of four leg muscles and perception of effort became lower in ECC than in CON cycling at most of five power outputs, while they were similar before.