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Does one plus one equal two? The influence of sequential single-leg cycling on cardiovascular disease risk

Gordon, Nicole (2018) Does one plus one equal two? The influence of sequential single-leg cycling on cardiovascular disease risk. PhD thesis, Murdoch University.

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Cardiovascular disease (CVD) is the leading cause of death worldwide. Regular exercise training can positively influence risk factors for CVD; however, the optimal training modality is unknown. Single-leg cycling allows greater leg blood flow and muscle-specific oxygen consumption resulting in higher localised intensity, when compared with double-leg cycling, and therefore could provide superior benefits to CVD risk factor profile. Within this thesis, three studies were conducted to examine the haemodynamic responses to sequential single-leg cycling (i.e. both legs exercised independently within a single session) and the chronic impact of this modality on common risk factors for CVD. Study One (Chapter Four) investigated the haemodynamic responses of the active and inactive legs during sequential single-leg (12 (six with one leg followed by six with the other leg) 1-min single-leg maximal effort intervals interspersed with one minute of passive recovery) and double-leg cycling (six 1-min double-leg maximal effort intervals interspersed with one minute of passive recovery) in a young healthy population. Study Two (Chapter Five) examined the acute central and peripheral haemodynamic responses of healthy middle-aged adults to sequential single-leg (20 (ten with each leg) 30-second single-leg intervals at a rating of perceived exertion (RPE) of 15-17 interspersed with 60 seconds passive recovery) and double-leg (ten 30-second double-leg intervals at a RPE of 15-17 interspersed with 60 seconds passive recovery) interval cycling. Study Three (Chapter Six) assessed the effects of eight weeks of cycle training, using moderate intensity double-leg continuous cycling (MCTDL; cycled continuously for 40 minutes at an RPE 11-13 using double-leg cycling), high intensity double-leg interval cycling (HITDL; twenty 30-second double-leg intervals at a RPE 15-17 separated by 60 seconds of passive recovery) or high intensity sequential single-leg interval cycling (HITSL: forty (twenty with each leg) 30-second single-leg intervals at a RPE of 15-17 interspersed with 60 seconds passive recovery), on CVD risk factors in healthy middle-aged adults.

In a young healthy population (Chapter Four), mean arterial pressure was higher during the initial compared with second set of single-leg intervals (108 ± 10 mmHg vs. 101 ± 10 mmHg; p<0.05). Furthermore, the pattern of change in muscle blood volume from the initial to second set of intervals was different (p<0.05) when the leg was active in the initial (-52.3 ± 111.6%) compared with second set (65.1 ± 152.9%). Differences in mean arterial pressure and blood volume distribution during sequential single-leg cycling indicates the presence of a leg order effect. Consistent with previous single-leg cycling studies in young healthy adults, the power output produced per leg was higher (p<0.01) during single-leg (176 ± 52 W) compared with double-leg (145 ± 38 W) interval cycling which confirms the higher localised intensity associated with this modality.

In contrast to findings in younger adults in Chapter Four, power output normalised to the active muscle mass was lower during single-leg compared with double-leg cycling (single-leg: 8.92 ± 1.74 W∙kg-1 and double-leg: 10.41 ± 3.22 W∙kg-1; p<0.05) in a healthy middle-aged population (Chapter Five). This was despite the greater normalised cardiac output (single-leg: 1407 ± 334 mL∙kg-1∙min-1 and double-leg: 850 ± 222 mL∙kg-1∙min-1; p<0.01) indicating surplus blood was available to the smaller active muscle mass. The dissociation between blood availability and power output is consistent with an ageing model characterised by a decrease in local oxygen delivery and distribution capability. However, in Chapter Six, when examined as an average of the entire eight-week intervention, the participants were able to maintain a higher normalised power output during HITSL compared with HITDL and MCTDL. These data indicate that older adults are likely to respond in a similar manner to younger cohorts; however, it may take multiple exercise sessions before differences in per leg power output are observed. From the data within this thesis, it is not possible to determine the exact number of exercise sessions required to familiarise older adults to this novel modality.

The findings presented in Chapter Six indicate that irrespective of modality, participants experienced improvements in fitness (22.3 ± 6.4 mL∙kg-1∙min-1 vs 24.9 ± 7.6 mL∙kg-1∙min-1; p<0.01), and reductions in waist-to-hip ratio (0.84 ± 0.09 vs 0.83 ± 0.09; p<0.01), resting blood pressure (systolic: 129 ± 11 mmHg vs 124 ± 12 mmHg; p<0.01-, diastolic: 79 ± 8 mmHg vs 76 ± 8 mmHg; p<0.02), total cholesterol (5.87 ± 1.17 mmol∙L-1 vs 5.55 ± 0.98 mmol∙L-1; p<0.01) and LDL cholesterol (3.70 ± 1.04 mmol∙L-1 vs 3.44 ± 0.84 mmol∙L-1; p<0.01) after the eight-week intervention. Additionally, the proportion of individuals in each condition who experienced clinically relevant changes in aerobic capacity, LDL cholesterol and blood pressure (i.e. those risk factors with published clinically relevant change scores) were assessed. During the double-leg cycling conditions (HITDL and MCTDL), more individuals demonstrated changes in aerobic capacity above the clinically relevant change score (i.e. changes associated with reductions in CVD morbidity and mortality) when compared with single-leg cycling. High intensity cycling (HITSL and HITDL) demonstrated a greater influence on LDL cholesterol when compared to moderate intensity cycling. Reductions in arterial blood pressure beyond clinically relevant change scores were more prevalent following HITSL compared with the double-leg cycling conditions (HITDL and MCTDL).

In conclusion, the findings presented in this thesis provide evidence for the therapeutic use of sequential single-leg cycling in healthy populations. Importantly, when using sequential single-leg cycling as a training modality, active leg order should be alternated in each training session due to potential alterations in acute cardiovascular and metabolic responses. Further, short-term exercise training of moderate or high intensity and using double-leg or single-leg cycling can positively influence risk factors for CVD. However, based on the proportion of individuals surpassing the clinically relevant change scores for select CVD risk factors, practitioners should focus their selection of exercise modality for the specific goals of the exercise intervention.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Psychology and Exercise Science
United Nations SDGs: Goal 3: Good Health and Well-Being
Supervisor(s): Peiffer, Jeremiah, Abbiss, Chris and Maiorana, Andrew
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