Edward C. Rhodes

Factors associated with exercise adherence among older adults. An individual perspective.

AbstractThis paper reviews the literature concerning factors at the individual level associated with regular exercise among older adults. Twenty-seven cross-sectional and 14 prospective/longitudinal studies met the inclusion criteria of a mean participant age of 65 years or older. The findings are summarised by demographics, exercise experience, exercise knowledge, physiological factors, psychological factors, activity preferences and perceived social influences. In general, education and exercise history correlate positively with regular exercise, while perceived physical frailty and poor health may provide the greatest barrier to exercise adoption and adherence in the elderly. Social-cognitive theories identify several constructs that correlate with the regular exercise behaviour of older adults, such as exercise attitude, perceived behavioural control/self-efficacy, perceived social support and perceived benefits/barriers to continued activity. As well, stage modelling may provide additional information about the readiness for regular exercise behaviour among older adults. However, relatively few studies among older adults exist compared with middle-aged and younger adults. Further, the majority of current research consists of cross-sectional designs or short prospective exercise trials among motivated volunteers that may lack external validity. Future research utilising longitudinal and prospective designs with representative samples of older adults will provide a better understanding of significant causal associations between individual factors and regular exercise behaviour.

Oxygen Uptake Kinetics During Exercise

The characteristics of oxygen uptake (V̇O2) kinetics differ with exercise intensity. When exercise is performed at a given work rate which is below lactate threshold (LT), V̇O2 increases exponentially to a steady-state level. Neither the slope of the increase in V̇O2 with respect to work rate nor the time constant of V̇O2 responses has been found to be a function of work rate within this domain, indicating a linear dynamic relationship between the V̇O2 and the work rate. However, some factors, such as physical training, age and pathological conditions can alter the V̇O2 kinetic responses at the onset of exercise. Regarding the control mechanism for exercise V̇O2 kinetics, 2 opposing hypotheses have been proposed. One of them suggests that the rate of the increase in V̇O2 at the onset of exercise is limited by the capacity of oxygen delivery to active muscle. The other suggests that the ability of the oxygen utilisation in exercising muscle acts as the rate-limiting step. This issue is still being debated.When exercise is performed at a work rate above LT, the V̇O2 kinetics become more complex. An additional component is developed after a few minutes of exercise. The slow component either delays the attainment of the steady-state V̇O2 or drives the V̇O2 to the maximum level, depending on exercise intensity. The magnitude of this slow component also depends on the duration of the exercise. The possible causes for the slow component of V̇O2 during heavy exercise include: (i) increases in blood lactate levels; (ii) increases in plasma epinephrine (adrenaline) levels; (iii) increased ventilatory work; (iv) elevation of body temperature; and (v) recruitment of type IIb fibres. Since 86% of the V̇O2 slow component is attributed to the exercising limbs, the major contributor is likely within the exercising muscle itself. During high intensity exercise an increase in the recruitment of low-efficiency type IIb fibres (the fibres involved in the slow component) can cause an increase in the oxygen cost of exercise. A change in the pattern of motor unit recruitment, and thus less activation of type IIb fibres, may also account for a large part of the reduction in the slow component of V̇O2 observed after physical training.

Effects of Creatine Supplementation on Exercise Performance

While creatine has been known to man since 1835, when a French scientist reported finding this constituent ofmeat, its presence in athletics as a performance enhancer is relatively new. Amid claims of increased power and strength, decreased performance time and increased muscle mass, creatine is being hailed as a true ergogenic aid. Creatinine is synthesised from the amino acids glycine, arginine and methionine in the kidneys, liver and pancreas, and is predominantly found in skeletal muscle, where it exists in 2 forms. Approximately 40% is in the free creatine form (Crfree),while the remaining 60%is in the phosphorylated form, creatine phosphate (CP). The daily turnover rate of approximately 2g per day is equally met via exogenous intake and endogenous synthesis. Although creatine concentration (Cr) is greater in fast twitch muscle fibres, slow twitch fibres have a greater resynthesis capability due to their increased aerobic capacity. There appears to be no significant difference between males and females in Cr, and training does not appear to effect Cr. The 4 roles in which creatine is involved during performance are temporal energy buffering, spatial energy buffering, proton buffering and glycolysis regulation. Creatine supplementation of 20g per day for at least 3 days has resulted in significant increases in total Cr for some individuals but not others, suggesting that there are ‘responders’ and ‘nonresponders’. These increases in total concentration among responders is greatest in individuals who have the lowest initial total Cr, such as vegetarians. Increased concentrations of both Crfree and CP are believed to aid performance by providing more short term energy, as well as increase the rate of resynthesis during rest intervals. Creatine supplementation does not appear to aid endurance and incremental type exercises, and may even be detrimental. Studies investigating the effects of creatine supplementation on short term, high intensity exercises have reported equivocal results, with approximately equal numbers reporting significant and nonsignificant results. The only side effect associated with creatine supplementation appears to be a small increase in body mass, which is due to either water retention or increased protein synthesis.

Maximal and ventilatory threshold responses to treadmill and water immersion running

This study compared the metabolic responses of 13 endurance runners, familiar with nonweight-bearing water immersion (WI) running, at ventilatory threshold (Tvent) and maximal effort (VO2max) for both treadmill and WI running performance. Oxygen consumption (VO2), ventilation (VE), heart-rate (HR), VE/VO2, respiratory exchange ratio (RER), perceived exertion (RPE), and stride frequency (SF) were measured at Tvent and VO2max. Paired t-tests revealed higher VO2max (59.7 vs 54.6 ml.kg.-1min-1), HRmax (190 vs 175 bpm), RERmax (1.20 vs 1.10), VO2 at Tvent (46.3 vs 42.8 ml.kg.-1min-1), HR at Tvent (165 vs 152 bpm) for treadmill versus WI running, respectively. Treadmill and WI VEmax (109.0 vs 105.8 l.min-1), RPEmax (20), VE at Tvent (66.4 vs 65.7 l.min-1), RER at Tvent (0.99 vs 0.98), RPE at Tvent (13 vs 12) were similar, as were blood lactate [BLa] values obtained at 30 s (10.4 vs 9.8 mmol.l-1) and 5 min (9.7 vs 9.2 mmol.l-1) post-test. SF values over time were higher on the treadmill. The lower WI VO2max with similar peak [BLa] and lower SF values suggests that the active musculature and muscle recruitment patterns differ in WI running due to the high viscosity friction of water, and the nonweight-bearing nature of WI running.

Factors Affecting Performance in an Ultraendurance Triathlon

AbstractIn the recent past, researchers have found many key physiological variables that correlate highly with endurance performance. These include maximal oxygen uptake (V̇O2max, anaerobic threshold (AT), economy of motion and the fractional utilisation of oxygen uptake (V̇O2). However, beyond typical endurance events such as the marathon, termed ‘ultraendurance’ (i.e. >4 hours), performance becomes harder to predict. The ultraendurance triathlon (UET) is a 3-sport event consisting of a 3.8km swim and a 180km cycle, followed by a 42.2km marathon run. It has been hypothesised that these triathletes ride at approximately their ventilatory threshold (Tvent) during the UET cycling phase. However, laboratory assessments of cycling time to exhaustion at a subject’s AT peak at 255 minutes. This suggests that the AT is too great an intensity to be maintained during a UET, and that other factors cause detriments in prolonged performance. Potential defeating factors include the provision of fuels and fluids due to finite gastric emptying rates causing changes in substrate utilisation, as well as fluid and electrolyte imbalances. Thus, an optimum ultraendurance intensity that may be relative to the AT intensity is needed to establish ultraendurance intensity guidelines. This optimal UET intensity could be referred to as the ultraendurance threshold.

Lipid Metabolism During Exercise

Fat is an extremely important substrate for muscle contraction, both at rest and during exercise. Triglycerides (TGs), stored in adipose tissue and within muscle fibres, are considered to be the main source of the free fatty acids (FFAs) oxidised during exercise. It is still unclear, however, how the use of these substrates is regulated during exercise. The regulation seems to be multifactoral and includes: (i) dietary and nutritional status; (ii) hormonal milieu; (iii) exercise mode, intensity and duration; and (iv) training status.On the other hand, the mechanism for FFA transport from its storage as triglycerides in adipose tissue and muscle to its place of utilisation in heart, skeletal muscle, kidney and liver is more clearly understood. It has been determined that the plasma FFA turnover rate is sufficiently rapid to account for most of the fat metabolised during low intensity exercise (25 to 40% V̇O2max). However, an exercise intensity of 65% V̇O2max results in a slight decrease in the amount of plasma FFA uptake by muscle tissue. Other studies have found that during prolonged exercise, muscle TGs become the predominant source of energy obtained from fat. Furthermore, it is widely documented that endurance activities increase the energy utilisation from fat while sparing carbohydrate sources. For example, during exercise on a cycle ergometer, nonplasma FFAs and plasma FFAs contribute 40%, and carbohydrates 60%, of the total calculated amount of energy expenditure before exercise and vice versa after exercise (60% nonplasma and plasma FFAs and 40% carbohydrates).Although it was many years before it was fully demonstrated, fat is now known to be transported in the blood as FFA bound to the protein carrier albumin. The mobilisation of FFA is primarily a function of sympathetic nervous activity directed towards the adipocytes, or the ‘fat pad’. This nervous activity can be direct or may be an effect of circulating catecholamines such as adrenaline (epinephrine). This article summarises the role of fat metabolism during exercise.

A Critical Review of the Literature on Ratings Scales for Perceived Exertion

SummaryThe study of human performance and perceived exertion during physical activity has been an area of considerable interest and research for over 50 years. This review considers the evidence of many investigators who have been researching the physiological basis as well as non-physiological basis for the ratings of perceived exertion.During low levels of activity, physical perception in the working muscles appears to be the primary stimulus for effort perception. When work intensity exceeds the lactate threshold, incremental elevations in blood lactate complement peripheral input from the neuro-muscular mechanisms. Once a critical absolute ventilatory threshold is reached, central input also contributes to effort perception. In most instances, peripheral input predominates over central cues, although it has been shown that pronounced central cues may dominate the perception of effort. Central (heart rate,V̇E,V̇O2) or local (muscle and blood lactate, adenosine triphosphate, creatine phosphokinase, glycogen) cues highlighted in these studies demonstrate both the complexity of effort perception, and the need for better understanding of the physiological components upon which it is based. Athletes have been shown to have a greater tendency to reduce perceptual ratings than their non-active counterparts. In view of these observations, it is apparent that a theoretical framework based upon physiological and psychological considerations may exist to support the concept of training-induced alterations in perceived exertion. This appears to be particularly true in higher ranges of exercise intensity. Part of the problem in reaching a conclusion on the issue of perceptual ratings trainability centres upon the agreement on what should be recognised as a significant decrement in perceived exertion.It is concluded that there is considerable variation in the findings of the literature and that any reported variations in performance may well be greatly influenced by intersubject variability, the type of exercise, and nutritional status of subject. Further research is required to understand this issue better.

Applied Physiology of Ice Hockey

SummaryToday’s elite hockey players are physically bigger and have improved levels of physiological fitness when compared with their predecessors. Correspondingly, previous ice hockey studies that have become widely referenced may have little relevance to current players and the way the game is presently played.A great need exists to apply exercise science to the game of ice hockey. Although much has been written about the physiology of ice hockey, there is little information based on well controlled studies. Particularly, there is a paucity of knowledge concerning optimal training schedules, training specificity, recovery profiles and seasonal detraining. Moreover, the reports that do exist have attempted to make comparisons across all levels of skill and talent. Thus, fundamental questions remain as to actual physiological exercise response and specialised training programmes for ice hockey players, particularly at the elite level.There is a demand for new properly designed experiments to find answers pertaining to the appropriate training methods for today’s ice hockey players. Future research directions should consider the relationships between performance and such variables as neuromuscular skills, strength, power, peripheral adaptations, travel, hydration, detraining and sport-specific training programmes. Incidence and severity of injury among ice hockey players in relation to fatigue and fitness must also be investigated. Much of the information currently used in ice hockey will remain speculative and anecdotal until these studies are conducted.

The Physiology of Rock Climbing

In general, elite climbers have been characterised as small in stature, with low percentage body fat and body mass. Currently, there are mixed conclusions surrounding body mass and composition, potentially because of variable subject ability, method of assessment and calculation. Muscular strength and endurance in rock climbers have been primarily measured on the forearm, hand and fingers via dynamometry. When absolute hand strength was assessed, there was little difference between climbers and the general population. When expressed in relation to body mass, elite-level climbers scored significantly higher, highlighting the potential importance of low body mass.Rock climbing is characterised by repeated bouts of isometric contractions. Hand grip endurance has been measured by both repeated isometric contractions and sustained contractions, at a percentage of maximum voluntary contraction. Exercise times to fatigue during repeated isometric contractions have been found to be significantly better in climbers when compared with sedentary individuals. However, during sustained contractions until exhaustion, climbers did not differ from the normal population, emphasising the importance of the ability to perform repeated isometric forearm contractions without fatigue becoming detrimental to performance.A decrease in handgrip strength and endurance has been related to an increase in blood lactate, with lactate levels increasing with the angle of climbing. Active recovery has been shown to provide a better rate of recovery and allows the body to return to its pre-exercised state quicker. It could be suggested that an increased ability to tolerate and remove lactic acid during climbing may be beneficial.Because of increased demand placed upon the upper body during climbing of increased difficulty, possessing greater strength and endurance in the arms and shoulders could be advantageous.Flexibility has not been identified as a necessary determinant of climbing success, although climbing-specific flexibility could be valuable to climbing performance.As the difficulty of climbing increases, so does oxygen uptake (V̇O2), energy expenditure and heart rate per metre of climb, with a disproportionate rise in heart rate compared with V̇O2. It was suggested that these may be due to a metaboreflex causing a sympathetically mediated pressor response. In addition, climbers had an attenuated blood pressure response to isometric handgrip exercises when compared with non-climbers, potentially because of reduced metabolite build-up causing less stimulation of the muscle metaboreflex.Training has been emphasised as an important component in climbing success, although there is little literature reviewing the influence of specific training components upon climbing performance.In summary, it appears that success in climbing is not related to individual physiological variables but is the result of a complex interaction of physiological and psychological factors.

A review of the concept of the heart rate deflection point.

AbstractThe heart rate deflection point (HRDP) is a downward or upward change from the linear HR-work relationship evinced during progressive incremental exercise testing. The HRDP is reported to be coincident with the anaerobic threshold. In 1982, Conconi and colleagues suggested that this phenomenon could be used as a noninvasive method to assess the anaerobic threshold. These researchers developed a field test to assess the HRDP, which has become popularised as the ‘Conconi test’. Concepts used to define and assess the anaerobic threshold as well as methodological procedures used to determine the HRDP are diverse in the literature and have contributed to controversy surrounding the HRDP concept. Although the HRDP may be assessed in either field or laboratory settings, the degree of HR deflection is highly dependent upon the type of protocol used. The validity of HRDP to assess the anaerobic threshold is uncertain, although a high degree of relationship exists between HRDP and the second lactate turnpoint. The HRDP appears to be reliable when a positive identification is made; however, not all studies report 100% reproducibility. Although the physiological mechanisms explaining the HRDP are unresolved, a relationship exists between the degree and direction of HRDP and left ventricular function. The HRDP has potential to be used for training regulation purposes. Clinically, it may be incorporated to set exercise intensity parameters for cardiac rehabilitation.