Twenty-five controlled trial studies (12 randomized studies [27, 29–38] and 13 non-randomized studies [28, 39–50]) were identified for the review.
Effects on cardiovascular function
Effects on cardio-respiratory fitness
Specific effects of cycle ergometer training (CET) on cardio-respiratory fitness were reported in eight of the 12 randomized studies [27, 29–35] (Table 1). Indeed, after a moderate endurance program on cycle ergometer, Lovell et al. [27, 29] noted a significant increase in VO2max (15 and 17 % respectively, p < 0.05) in the active group compared to the control group. Similarly, in older patients over 70, Buchner et al.  reported a 9 % increase in VO2max (p < 0.05) after 78 endurance training sessions, with no significant change in the control group. Older subjects with a lower baseline VO2max showed the greatest improvement in VO2max (+29 %, p < 0.05) after CET, as shown by Babcock et al. . In a small group of older people, Malbut et al.  reported a 15 % increase in VO2max among women, and no significant change among men, after a 24-week program of CET at 75–80 % of VO2max. In two small randomized studies, Coker et al. [33, 34] observed a similar increase in aerobic fitness in both moderate and intermittent exercise groups as evidenced by a respective increase of 14 % and 21 % in VO2max, as the result of CET. Conversely, Mangione et al. , reported no significant change in VO2max in older patients in both high and low intensity cycle training groups.
Concerning the non-randomized studies, 11 of the 13 studies were conclusive [28, 40–48] (Table 1). A recent study by Vogel et al.  reported that a short-term intermittent cycling exercise program (36 min per session, 2 times per week for 9 weeks) led to a significant increase in VO2max (16.6 % and 8.9 % in older women and men respectively, all p < 0.05). Harber et al.  reported a significant improvement (29 %, p < 0.05) in the VO2max of older adults after 12 weeks of CET. In a small study, Perini et al.  also reported an 18 % (p < 0.05) increase in VO2max after 8 weeks of CET. Other data suggested that CET in people over 70 resulted in an 11 % (p < 0.01) increase in VO2max . Moreover, short-term CET led to a significant 16 % (p < 0.001) improvement in VO2max in 188 older subjects (73 ± 5 years old) . Using data from two studies including older patients, Charifi et al. [44, 45] observed a 13.5 % increase in VO2max (p < 0.05), after 56 sessions of CET. In a small study involving six older subjects (74 ± 2 years), Sial et al.  reported a 21 % increase in VO2max (p < 0.01) after 16 weeks of CET at 70–85 % of maximal heart rate (HRmax). Following 14 weeks of CET, Pichot et al.  observed an 18.6 % increase in the VO2max (p < 0.01) among older adults over 70. Finally in a small study, Bell et al.  reported a significant 16 % increase in VO2max after 36 sessions of CET at 70–85 % of VO2max performed using a single leg.
According to these studies, moderate to high intensity of personalized CET, i.e., 30 min a day at least twice a week for a period of nine weeks seems to be useful for improving cardio-respiratory fitness among older adults over 70.
Effects on blood pressure
The benefits of CET on blood pressure in older subjects over 70 are less consistent and were reported in five studies [36, 37, 41, 47, 49] (Table 1). In a small randomized trial on healthy normotensive older patients, Nickel et al.  noted a significant decrease in systolic blood pressure (SBP) by 8 % after 15 min and in diastolic blood pressure (DBP) by 4 % after 24 h of CET at 50 % of heart rate reserve (HRR) in the active group compared to the control group (121 ± 12 vs. 131 ± 16 mmHg; p < 0.05) and (72 ± 8 vs. 69 ± 7 mmHg; p < 0.05), respectively. In a small pilot study including 15 older subjects, Perini et al.  observed a significant reduction in resting systolic (16 and 14 %, p = 0.001) and diastolic blood pressure (13 and 11 %, p = 0.004) in older men and women respectively, with no significant effects on SBP and DBP on recovery after 8 weeks of CET. However, three other studies [37, 47, 49] did not observe any significant change in SBP and DBP following CET.
Based on these studies, short-term CET seems to be associated in some extent with a significant decrease in SBP by 8–16 % and in DBP by 4–13 % in older adults over 70. This can be associated with a decrease in cardiac morbidity, stroke, and all-cause mortality.
Effects on endurance parameters
In this review, eight studies have shown that CET leads to significant improvement in endurance parameters of older adults over 70 [28, 31, 32, 37, 38, 42, 43, 49] (Table 1). Vogel et al.  reported a significant increase in the first ventilatory threshold (VT1) by 27.9 and 21.2 % (all, p < 0.05), respectively, in older men and women. Likewise, these authors reported a significant decrease in the heart rate (HR) at pre-training VT1 (−6.2 and −5.2 %, respectively; p < 0.05) as well as in lactate concentrations at pre-training maximal tolerated power (MTP) (−23.4 and −20 %, respectively; p < 0.05), after nine weeks of CET. In a small group of older people, Morris et al.  reported that at the same relative intensity (50 % or 70 % of VO2max), interval exercise training resulted in a significant reduction in HR and oxygen uptake as opposed to continuous exercise training (p < 0.01). In a small group of older adults (72 ± 4.4 years old), Babcock et al.  reported a 21 % (p < 0.05) increase in oxygen uptake (VO2) at VT1. However, they did not report any significant change in HR at VT1 after 72 exercise sessions of CET. In another study in older men and women, Malbut et al.  reported a significant decrease in HR at VO210 (heart rate at an oxygen consumption of 10 ml/kg/min) by 8 % (p < 0.05) and 15 % (p < 0.01) respectively, after 24 weeks of CET. Temfemo et al.  reported a significant increase in VT1 (17 %, p < 0.05) in older patients after 8 weeks of CET at VT1. Finally, Schocken et al. , Haber et al.  and Finucane et al.  reported significant 10 % (p < 0.008), 16 and 16.5 % (p < 0.01) respective increases in the maximum workload, after 12 weeks of CET among older patients.
Based on these studies, short to medium-term of CET at an intensity of VT1 appears to be an optimal way of improving endurance parameters among older adults over 70, specifically through an increase in the oxygen uptake by 21 %, in the mean VT1 and maximum workload by 22 and 14 %, respectively. These improvements are important for seniors, and may contribute towards a better quality of life.
Effects on metabolic outcomes
Effects on body composition
In this review, the effects of CET on body composition in older patients over 70 were evaluated in eight studies [27, 33, 34, 37, 40, 41, 46, 51] (Table 2). Specifically, a 16-week CET program at 50–70 % of VO2max resulted in a significant decrease in body mass and in the percentage of body fat (−2.6 and −5 % respectively; p < 0.05), with no significant change in fat-free mass in older patients . In 100 healthy older adults, Finucane et al.  reported a significant decrease in total body mass (−10 %, p = 0.007), BMI (−0.4 %, p = 0.03), in waist circumference (−0.8 %, p = 0.02) and in intrahepatic lipids (−54 %, p = 0.024) in the exercise group compared with controls, whereas the same authors reported no significant alteration in fat mass and fat-free mass in the two groups after 12 weeks at 50–70 % of maximum power (Pmax) of CET. However, there is evidence that the aforementioned exercise-induced adaptations can also occur independently of weight loss . For example, Harber et al.  reported a significant decrease in fat mass (−3.9 %, p < 0.01) and in percentage body fat (−2.4 %, p < 0.01) with a significant increase in fat-free mass (−0.9 %, p < 0.01), without an overall decrease in body weight following 12-week of CET at 60 % of Pmax. Likewise, 16 weeks of CET at 70–85 % of HRmax in older patients improved fat-free mass by 2 % (p < 0.05) without an overall decrease in body weight . Conversely, three studies reported no significant change in body composition after 12 weeks of CET [33, 34, 41].
These outcomes suggest that 12–16 weeks of moderate to high intensity of CET may be an appropriate way to improve the body composition among older adults over 70, specifically by a significant decrease in the mean percentage of body fat and of body mass by 3.7 and 6.3 % respectively, and particularly by maintaining free-fat mass. These data highlighted the importance of CET when designing weight management strategies among older patients over 70.
Effects on metabolic disorders
Specific effects of CET on metabolic disorders were reported in 4 studies [33, 34, 37, 46] (Table 2). Indeed, Sial et al.  observed after 16 weeks of CET, a significant increase in the average rate of fat oxidation during exercise (33 %, p = 0.002), and a significant decrease in the average rate of carbohydrate oxidation during exercise (−19 %, p = 0.003). However, these authors did not report any significant change in the glycerol rate of appearance (Ra) and in the free fatty acid (FFA) rate of disappearance during exercise, but did report a significant 11 % decrease in glucose Ra after the training program (p = 0.01) among older adults. Further, 12 weeks of CET 4–5 times per week (40 min per session) led to a significant increase in insulin-stimulated glucose disposal (ISGD) (28 %, p < 0.05) as well as in non-oxidative glucose disposal (NOGD) (30 %, p < 0.05) only in a high-intensity (HI) training group, with no significant change in the moderate-intensity (MI) training group .
In another study, 12 weeks of CET led to a slight (non-significant) increase in plasma adiponectin in both MI and HI training groups . Conversely, Finucane et al.  reported no differences in fasting glucose, oral glucose insulin sensitivity and HbA1c between the training and control groups after 12 weeks of CET.
According to the above studies, short-term of CET can be in some extent an efficient strategy to prevent the metabolic disorders among older adults over 70, specifically through an increase in the fat oxidation and a decrease in the carbohydrate metabolism during exercise as well as by enhancing overall glucose disposal which have a positive effect on the regulation of glucose metabolism. This could have important clinical implications by increasing exercise capacity in this population.
Effects on endocrine function
Only two of the studies reviewed analyzed the effects of CET on endocrine function in older patients [29, 50] (Table 2). Zmuda et al.  reported a significant increase in serum testosterone, sex hormone-binding globulin (SHBG), total serum protein and the free testosterone index (39, 19, 13 and 23 % respectively; all p < 0.01) with no significant change in LH concentrations, during 60 min of CET at 50–80 % of HRR. After 48 sessions of CET, Lovell et al.  observed a significant 14 % increase in plasma concentration of testosterone, and of 15 % in free testosterone concentration (all, p < 0.05), with no significant change in growth hormone (GH), insulin like growth factor-1 (IGF-1) or in SHBG concentration.
According to these two reports, CET can have significant effects on the major male reproductive hormone, mainly through an improvement in the concentration of testosterone in plasma, which, in turn, may have cardiovascular protective effects in older adults over 70.
Effects on functional status
Effects on muscle strength
This review shows that CET may be a sufficient stimulus to increase muscle strength and power in older patients over 70 through seven studies [27, 29, 30, 32, 40, 41] (Table 3). For example, after 48 sessions of CET at 50–70 % of VO2max (30–45 min/session), Lovell et al.  reported a significant increase in multiple muscle strength outcomes in older adults (i.e., leg strength (18 %), leg power (12 %), upper leg muscle mass (7 %), and total leg muscle mass (7 %), all p < 0.05). Similarly, Lovell et al.  observed a significant 18 % (p < 0.05) increase in leg strength and a 13.5 % (p < 0.05) increase in peak power after 16 weeks of CET in older patients. A 12-week exercise program (cycling 3–4 times/week, 20–45 min/session at 60–80 % of HRR) led to an 11 % improvement in quadriceps muscle volume, a 23 % increase in knee extensor power and a 31 % increase in knee extensor peak isometric force, as well as a 12 % increase in normalized power and a 20 % increase in normalized force (all, p < 0.05) . Nine months of CET three times per week (∼35 min per session) increased the strength of the knee extensor by 10 % (p < 0.05), with no significant change in the strength of the other muscles . Conversely, Perini et al.  did not report any significant change in quadriceps isometric strength or endurance after 8 weeks of CET. Likewise, Denison et al. reported no significant change between training and control groups in maximum grip strength after 12 weeks of CET at 50–70 of HRmax. Finally, Malbut et al.  observed no effect of CET in isometric knee extensor strength, isometric elbow flexor strength or lower limb extensor power among older patients.
To summarize the above data, CET for 20–45 min, three times a week for 12–16 weeks at 50–70 % of VO2max, is an efficient way of maintaining and improving muscle strength among older adults over 70, specifically through the development of leg and knee extension strength as well as the strength of the upper and total leg muscle mass.
Conflicting results have been reported concerning the effect of CET on the physical performance of older patients over 70 [30, 35] (Table 3). In a randomized controlled trial, Buchner et al.  did not observe any significant improvement in gait and balance test, after 24 weeks of CET. Denison et al., reported only a significant decrease in the 6 m timed up and go test (TUG) by 7 % (p = 0.04) in the training group compared to the control group, with no significant differences between groups in 3 m walk, eyes closed one-legged balance, and chair rise test after 12-week of CET. In contrast, ten weeks of CET led to a significant improvement in chair rise time (−22 %, p < 0.001) and in the 6-minute walk test (9 %, p < 0.001) among older frail adults .
According to these three reports, short to medium-term CET modestly improve physical performance of older patients over 70, specifically through a decrease in the TUG as well as in chair raise time and an increase in the 6-minute walk test. Nevertheless, further studies are needed to investigate the effects of long-term CET on the physical performance of this aged population.
Effect on cognitive function
To our knowledge, only one study has shown that CET can help improve cognition in frail older adults over 70 (Table 4). Indeed, Palleschi et al.  reported a significant improvement in cognitive performance, in particular an increase in the test of attentional matrix, the verbal span test, the supraverbal span test and the mini mental state examination (22, 34, 71 and 12 % respectively; p < 0.0001), after 3 months of CET in a small group of older patients affected by Alzheimer’s senile dementia.
According to the outcomes of this study, CET could be promoted in older adults as a cost-effective, efficient, and viable way to reduce cognitive dysfunction, but further studies are needed to confirm these finding among older patients over 70.