Components of fitness

The cardiorespiratory system and skeletal muscle constitute the most important physiological systems that define and influence physical fitness. The capacity of these systems is at the centre of the physical fitness concept because they interact to generate external work for all physical activities (USDHHS 2008).

This is why, in this book, we shall focus on aerobic fitness, muscle strength and muscle power:

The successful performance of any physical activity is not just about muscular work. Other parameters are involved which include motor control, balance, flexibility (range of motion about a joint) and body composition (e.g. lean body mass).

Plasticity of fitness

In healthy people, physical fitness parameters show considerable variation and plasticity that is the ability to change and adapt (Fig. 4.1). Key factors in influencing fitness and plasticity are:

Fig 4.1 Age- and gender-related decline in cardiorespiratory fitness ( l; Shvartz and Reibold 1990) ( * ; Malbut et al. 2002) and musculoskeletal fitness ( l; Skelton et al. 1999) ( * ; Skelton et al. 1994) in healthy people aged 50 years and older. Functional thresholds (—) are marked on these data to indicate when low fitness may limit certain activities (Allied Dunbar National Fitness Survey 1992, Ainsworth et al. 2000) or threaten independence (Shephard 2009). Data points are means and error bars represent 2 standard deviations.

Functional importance of fitness

Low physical fitness may be insufficient to meet the energetic demands of certain activities, thus rendering them fatiguing and uncomfortable (Fig. 4.1). For example, muscle strength and power of the lower limbs both predict the ability to perform functional activities such as stair climbing, chair rising and walking speed, but power is the strongest predictor (Cuoco et al. 2004, Puthoff and Nielsen 2007). ‘Thresholds’ exist for physical fitness below which independence is threatened (Fig. 4.2). For examplepeak values below 15–18   ml   ·   kg^-1   ·   min^-1 (Shephard 2009; Fig. 4.1) and muscle strength of the hip flexors strength below 2.3   N   ·   kg^-1 (Hasegawa et al. 2008) are both associated with loss of independence. Therefore, as fitness declines (for any reason) the likelihood of activity limitations and loss of independence increases, and individuals are vulnerable to the inevitable effects of further age-related decline.

Fig 4.2 Physical fitness and function through the lifespan (—) showing the age-related decline seen during adulthood and the implications this may have for loss of independence in later life (Young 1986). The arrows indicate how factors such as gender, health status and physical activity level may influence fitness and function positively (↑) and negatively (↓) and in turn hasten or delay age-related loss of independence.

Post-stroke cardiorespiratory fitness

Measures of cardiorespiratory fitness in ambulatory stroke survivors have shown thatpeak is half (50% to 60%) that expected in healthy people matched for age and gender (Fig. 4.3A). The typicalpeak observed was ~15   ml   ·   kg^-1   ·   min^-1, which corresponds to that implicated in loss of independence in elderly people (15–18   ml   ·   kg^-1   ·   min^-1; Shephard 2009). The low values suggest some everyday activities would be difficult to perform since they recruit a high proportion of thepeak, resulting in either fatigue or the need to slow down or modify the activity (Fig. 4.3B).

Fig 4.3 The averagepeak of stroke patients (19 studies; n=714, not cited) in relation to time since stroke, expressed (A) relative to a healthy, untrained age- and gender-matched population (Shvartz and Reibold 1990), and (B) corrected for body mass in relation to the energetic cost of selected physical activities (Ainsworth et al. 2000) and a proposed boundary in(around 15 to 18   ml   ·   kg^-1   ·   min^-1) below which a loss of independence is implicated in elderly people (Shephard 2009). Each data point is the meanvalue reported by each study and the error bars represent the standard deviation.

Abnormal gait and low gait speed are common post-stroke problems caused by factors such as abnormal patterns of movement, use of walking aids, hemiparesis, poor flexibility, contractures, abnormal muscle tone, antagonist coactivation and poor balance. One consequence is an increased energy expenditure which does not contribute to locomotion. Thus thecost per unit distance walked can be several times greater than in healthy people (da Cunha et al. 2002, David et al. 2006, Platts et al. 2006), even after controlling for the confounding effect of a lower gait speed. Peakis half that expected in healthy people, yet thecost of walking is typically double. This means that the high cost of even slow walking may involve drawing on a high proportion of the already diminished maximal, leaving little in ‘reserve’. One consequence is that walking is fatiguing and slow and there is little leeway for further deterioration in fitness before walking becomes impossible.

Post-stroke muscle strength

Observational studies comparing the isometric strength of stroke survivors with healthy adults show clear evidence of the muscle weakness, especially on the side of body affected by stroke. This is a defining feature of many types of stroke (Table 4.1).

Table 4.1 Studies comparing bilateral measures of isometric muscle strength in stroke patients with age-matched healthy control groups

Related posts:

Models of Exercise after Stroke service design Evaluating exercise and fitness training after stroke: outcome assessment What is a stroke? Guidelines for Exercise after Stroke service design Communication: getting it right Designing and delivering an exercise and fitness training programme for stroke survivors

Stay updated, free articles. Join our Telegram channel

Join