The light and dark sides of perfectionism : implications for health and well-being

The present work presents two studies that examined the association of perfectionism, operationally defined by Hewi t t and Fl e t t ' s (1991) multidimensional mode l of perfectionism, with health and subjective well-being (SWB). The underlying question of this research was whether perfectionism could be beneficial as well as detrimental to health and well-being, as this is one of the mos t highly debated questions in the current literature. In samples of relatively healthy university students (n = 538) and community adults suffering from various chronic illnesses (n = 772), results from Study One indicated that socially prescribed perfectionism (SPP) is directly associated wi th poor e r he a l th and well-being. Results further showed f rom a personcentered perspective that there is a l a rge group of individuals wi th high levels of SPP and that i t is indeed these individuals who reported the poorest health and lowe s t levels of well-being. Other-oriented perfectionism was found to be unrelated to health and SWB. Findings revealed that when perfectionism is self-imposed (i.e., self-oriented perfectionism; SOP), i t is neither healthy nor unhealthy in an absolute sense. From the variable-centered perspective, this conclusion was supported by the f a c t tha t SOP was associated wi th both positive (e.g., be t t e r mental health and highe r levels of SWB in the student sample), and nega t ive correlates (e.g., higher levels of negative affect, stress, and neuroticism in both samples). Evidence f rom the chronically-ill sample further substantiated this conclusion by showing that there may be an optimal level of SOP, because mode r a t e levels of SOP we r e found to be associated with be t t e r health and highe r levels of SWB, whereas levels tha t we r e too low or too high we r e found to be associated with poor e r health and lowe r levels of SWB. Findings f rom the person-centered approach we r e particularly informative, in that they not only demonstrated tha t unique profiles of

Force potentiation as a modulator of contractile performance: Implications for control of skeletal muscle force and energetics of work

This thesis investigated the modulation of dynamic contractile function and energetics of work by posttetanic potentiation (PTP). Mechanical experiments were conducted in vitro using software-controlled protocols to stimulate/determine contractile function during ramp shortening, and muscles were frozen during parallel incubations for biochemical analysis. The central feature of this research was the comparison of fast hindlimb muscles from wildtype and skeletal myosin light chain kinase knockout (skMLCK-/-) mice that does not express the primary mechanism for PTP: myosin regulatory light chain (RLC) phosphorylation. In contrast to smooth/cardiac muscles where RLC phosphorylation is indispensable, its precise physiological role in skeletal muscle is unclear. It was initially determined that tetanic potentiation was shortening speed dependent, and this sensitivity of the PTP mechanism to muscle shortening extended the stimulation frequency domain over which PTP was manifest. Thus, the physiological utility of RLC phosphorylation to augment contractile function in vivo may be more extensive than previously considered. Subsequent experiments studied the contraction-type dependence for PTP and demonstrated that the enhancement of contractile function was dependent on force level. Surprisingly, in the absence of RLC phosphorylation, skMLCK-/- muscles exhibited significant concentric PTP; consequently, up to ~50% of the dynamic PTP response in wildtype muscle may be attributed to an alternate mechanism. When the interaction of PTP and the catchlike property (CLP) was examined, we determined that unlike the acute augmentation of peak force by the CLP, RLC phosphorylation produced a longer-lasting enhancement of force and work in the potentiated state. Nevertheless, despite the apparent interference between these mechanisms, both offer physiological utility and may be complementary in achieving optimal contractile function in vivo. Finally, when the energetic implications of PTP were explored, we determined that during a brief period of repetitive concentric activation, total work performed was ~60% greater in wildtype vs. skMLCK-/- muscles but there was no genotype difference in High-Energy Phosphate Consumption or Economy (i.e. HEPC: work). In summary, this thesis provides novel insight into the modulatory effects of PTP and RLC phosphorylation, and through the observation of alternative mechanisms for PTP we further develop our understanding of the history-dependence of fast skeletal muscle function.