Abstract
In this study, healthy young males were randomized into groups with moderate intensity training (n = 24), high intensity training (n = 24) and utmost intensity training (n = 24). At the end of 8-week training period, HRV measurements demonstrated a marked increase of RMSSD (P = 0.003), PNN50 (P = 0.002), HF (P = 0.002), SDNN (P = 0.002) and LF (P = 0.003) in the moderate intensity group and a decreasing tendency in LFn and LF/HF; however, in the utmost intensity group HFn (P = 0.012) decreased prominently while its LF (P = 0.032), LFn (P = 0.039) and LF/HF (P = 0.015) increased significantly. Nevertheless marked changes were not found in the above indexes of the high intensity group. While resting HR of the three groups declined significantly at the end of 8 weeks (P was 0.001, 0.0001 and 0.001 respectively); RMSSD, PNN50, HF, LF and SDNN were significantly higher in the moderate intensity group than in the other two groups (P P = 0.012) was significantly lower but its LFn and LF/HF were markedly higher (P was 0.025 and 0.015 respectively); LF/HF of both the high and utmost intensity group was significantly higher (P was 0.033 and 0.037 respectively). Despite a significant reduction of plasma NE in all the three groups at the end of 8-week training period (P was 0.016, 0, 0.031 respectively), plasma NE level of moderate and high intensity group was much lower than that of the utmost intensity group (P was 0.001, 0 respectively). Utmost and moderate endurance training results in altered sympathetic and parasympathetic balance towards sympathetic dominance and parasympathetic dominance respectively; whereas high intensity endurance training almost has no effect on ANS function. CPT and HUTT reveal the potential danger posed by utmost intensity endurance training.
Highlights
Autonomic nervous system (ANS) has the function of widely automatic regulation of heart, smooth muscle and endocrine gland
In the moderate intensity group a prominent increase in PNN50 and LF (P was 0.022 and 0.011 respectively) and a marked decrease in resting HR (P = 0.00) were noted from pre to mid, but no significant changes occurred to the indexes of other groups
The moderate intensity group showed a significant increase in RMSSD, PNN50, HF, SDNN and LF (P was 0.003, 0.002, 0.002, 0.002, 0.003 respectively), an increasing tendency in HFn but a decreasing tendency in LFn and LF/HF; the utmost intensity group demonstrated a significant reduction in HFn (P = 0.012), a marked increase in LF, LFn and LF/HF (P was 0.032, 0.039, 0.015 respectively) and no significant changes in HF, RMSSD, PNN50
Summary
Autonomic nervous system (ANS) has the function of widely automatic regulation of heart, smooth muscle and endocrine gland. Cold stimulus activates SN, whose nerve ending releases norepinephrine (NE); on the other hand, it paralyzes PN and maximizes epinephrine effect. All these lead to vasoconstriction and elevated BP [5] [6]. Elevated BP (SBP and/or DBP > 20 mmHg) suggests overactive SN, weak autonomic regulation on the cardiovascular system and susceptibility to disease [7]-[9]. Recent researches reveal how HR reacts to stress during CPT reflects ANS regulation [10] [11]
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