The Cardiovascular Response to Interval Exercise Is Modified by the Contraction Type and Training in Proportion to Metabolic Stress of Recruited Muscle Groups

Abstract

Background: Conventional forms of endurance training based on shortening contractions improve aerobic capacity but elicit a detriment of muscle strength. We hypothesized that eccentric interval training, loading muscle during the lengthening phase of contraction, overcome this interference and potentially adverse cardiovascular reactions, enhancing both muscle metabolism and strength, in association with the stress experienced during exercise.

Methods: Twelve healthy participants completed an eight-week program of work-matched progressive interval-type pedaling exercise on a soft robot under predominately concentric or eccentric load.

Results: Eccentric interval training specifically enhanced the peak power of positive anaerobic contractions (+28%), mitigated the strain on muscle's aerobic metabolism, and lowered hemodynamic stress during interval exercise, concomitant with a lowered contribution of positive work to the target output. Concentric training alone lowered blood glucose concentration during interval exercise and mitigated heart rate and blood lactate concentration during ramp exercise. Training-induced adjustments for lactate and positive peak power were independently correlated (p < 0.05, |r| > 0.7) with indices of metabolic and mechanical muscle stress during exercise.

Discussion: Task-specific improvements in strength and muscle's metabolic capacity were induced with eccentric interval exercise lowering cardiovascular risk factors, except for blood glucose concentration, possibly through altered neuromuscular coordination.

Keywords: concentric; eccentric; muscle contraction.

Figure 1

Power output and muscle oxygen saturation during workload-matched concentric and eccentric type of interval exercise. (A,B) Example of the power output being produced by one subject during one interval of concentric (A) and eccentric (B) interval exercise, respectively, before training. (C–F) Positive and negative work being performed by the left leg of one subject during all intervals of a session of concentric (C) and eccentric (D) interval exercise and the resulting effects on muscle oxygen saturation and hemoglobin concentration in m. vastus lateralis (E,F) for one leg before training.

Figure 2

Temporal response of perceived exertion and heart rate during concentric and eccentric type of interval exercise. Line graph with whiskers indicating mean values ± SE for perceived exertion (A,B) and heart rate (C,D) as measured each 2 min during the interval-type pedaling exercise before and after the eight weeks of training of the two groups under the concentric (A,C) or eccentric (B,D) contraction protocol. The rest and pedaling phase of the respective concentric and eccentric interval exercise is exemplarily indicated in panels A and B. *, p < 0.05 vs. 0 min. ‡, p < 0.05 vs. concentric. Repeated-measures ANOVA with a post-hoc test of least significant difference.

Figure 3

Temporal response of systolic and diastolic blood pressure during concentric and eccentric type of interval exercise. Line graph with whiskers indicating mean values ± SE for diastolic blood pressure (A,B) and systolic blood pressure (C,D) as measured each 2 min during the interval-type pedaling exercise before and after the eight weeks of training under the concentric (A,C) or eccentric (B,D) contraction group. *, p < 0.05 vs. 0 min. ‡, p < 0.05 vs. concentric. $ p < 0.05 vs. pre. Repeated-measures ANOVA with a post-hoc test of least significant difference.

Figure 4

Temporal response of blood glucose and lactate concentration during concentric and eccentric type of interval exercise. Line graph with whiskers indicating mean values ± SE for blood glucose concentration (A,B) and blood lactate concentration (C,D) as measured each 2 min in the two groups during the interval-type pedaling exercise before and after the eight weeks of training under the concentric (A,C) or eccentric (B,D) contraction protocol. *, p < 0.05 vs. 0 min. ‡, p < 0.05 vs. concentric. $, vs. pre. Repeated-measures ANOVA with post-hoc test of least significant difference.

Figure 5

Connectivity of correlations between stress during the stimulus of interval exercise and the adjustments with training. Network display of the 131 linear relationships between indices of metabolic and mechanical stress during interval exercise and training-induced adjustments (nodes) for Pearson correlations, which passed a threshold of |r| > 0.70 and p < 0.05. Straight red and stippled blue lines, respectively, indicate positive and negative correlations. The strength of the correlation is indicated by the thickness of the lines connecting two nodes. Red and orange colored nodes highlight stress during the first and last session of interval exercise, respectively. Green colored nodes emphasize training-induced fold changes. Note the high connectivity with parameters demonstrating an interaction effect of interval training × the contraction group with the reddish-indicated indices of stress during interval exercise that define (highlighted) entities. This comprises selective correlations of the green-highlighted fold changes in positive peak power and the corresponding rate of force development (black arrows), the fold changes for the AUC of the blood lactate concentration during the ramp test (red arrow) or during interval exercise (green arrow), with the AUC of the perceived exertion, heart rate, the systolic blood pressure, the hemoglobin accruing in m. gastrocnemius, and the oxygen deficit in m. vastus lateralis, and the average power during interval exercise. For the ramp exercise, only the AUCs over the same duration of exercise before training were considered. Abbreviation code: _A, AUC during exercise; BPdia, diastolic blood pressure; BPsys, systolic blood pressure; bm, body mass; DO2, oxygen deficit; DO2_ave, average oxygen deficit; fold, post vs. pre ratio; gas, m. gastrocnemius; glucose, blood glucose concentration; HR, heart rate; _I, during interval exercise; L, _S, number of intervals (sets); left leg; lactate, blood lactate concentration; nPP, negative peak power; nW, negative work; P_ave, average power; post, after training; PPO, peak power output during the ramp test; pPP, positive peak power; pre, prior to training; pW, positive work; rPP, reactive peak power; R, right leg; _R, during ramp test; pRFD, rate of force development during the development of positive peak power; RPE, rate of perceived exertion; sP, target power per PPO; _t, exercise duration; tHb, concentration of total hemoglobin; vas, m. vastus lateralis; tHb_ave, average concentration of total hemoglobin; VO2peak, peak oxygen uptake.