Physical activity can have a beneficial effect on health and fitness [1, 2]. Unfortunately, most adults are insufficiently active [3], below the recommended 150 min physical activity of moderate intensity or 75 min of vigorous intensity per week [4].

In the last decades, research has indicated an increase in exercise training during leisure time [5], and a reduction in household- [6], work-, and transport-related physical activity [5]. Promotion of transport-related physical activity has traditionally focused on walking and cycling [7]. Meanwhile, electric assisted bicycles (E-bikes) have become increasingly popular [8]. E-bike users have reported advantages such as higher speed with less effort, reduced travel time and easier to climb hills compared to conventional bicycles [9, 10]. In Europe, E-bikes provide electrical assistance only when the bike rider is pedalling [11], thus is partly human powered. Moreover, E-bikes seem to be highly used for commuting purposes [10, 12–14]; therefore, it is essential to establish whether cycling with an E-bike can be health-enhancing, which depends on duration and intensity of physical activity [15].

Intensity can be measured as relative, such as percentage of maximal oxygen uptake (\( \overset{.}{\mathrm{V}}{\mathrm{O}}_2 \max \)) or absolute as metabolic equivalent of tasks (METs), where one MET is defined as resting metabolic rate (RMR). However, without direct measurements, RMR is usually replaced by a 1-MET reference value of 3.5 ml O₂/kg/min [16]. Intensity when riding a conventional bicycle has been classified as vigorous, ranging from 6.4 to 8.2 METs [16–19]. Recent studies on E-bikes have reported somewhat lower intensity, ranging from 4.1 to 6.1 METs [19–22]. Some studies [20–22] have compared cycling with no- and maximal electrical power; however, an E-bike is heavier than a conventional bicycle and therefore E-biking with the power switched off does not fairly represent cycling on a conventional bicycle [8, 23].

Gojanovic et. al.[19] investigated direct comparisons between cycling on an E-bike and a conventional bicycle. They found lower exercise intensity, measured as percentage of \( \overset{.}{\mathrm{V}}{\mathrm{O}}_2 \max \), on an E-bike (55%) compared with a conventional bicycle (73%) on an uphill route. However, the lower cycling intensity is likely to vary according to topography. In addition, previous studies [19–22] have estimated METs based on the standard 1-MET of 3.5 ml O₂/kg/min. Since RMR may be influenced by age, gender, fat-free mass, body mass index (BMI) and fitness level [24, 25], direct measurements are preferred.

The objectives of the present study were to compare time spent cycling, exercise intensity, and time spent in moderate- (MPA) and vigorous intensity physical activity (VPA) when cycling on an E-bike and a conventional bicycle on two “cycling-to-work” routes with differences in topography, defined as a hilly and a flat route.

In the present study, comparing e-biking to conventional bicycling on two different routes simulating relevant cycling to work options, e-biking was faster and less intensive than conventional bicycling, especially on the hilly route. However, 95% of time spent biking, both for e-bike and conventional bike, were considered to be MVPA.

E-biking were faster than conventional bicycling, and reduced the time cycling with almost 30% in the hilly route. These results support the findings from previous studies regarding lower trip duration with an E-bike compared with a conventional bicycle [19, 30, 31], due to a higher speed. Gojanovic et al. [19] observed that when riding an E-bike, speed was on average 6 km/h higher than on a conventional bicycle, on the same route, similar to the 5 km/t in the present study. Furthermore, observational studies found on average 2 km/h higher speed in E-bike cyclists compared with individuals travelling by conventional bicycles [30, 31]. Schleinitz et al. [30] also illustrated that age, road gradient, and bicycle infrastructure may influence differences in cycling speed and trip duration between E-bikes and conventional bicycles.

E-biking was less intense than conventional bicycling, both relative (a 17% lower \( \overset{.}{\mathrm{V}}{\mathrm{O}}_2 \max \)) and absolute (36% lower time spent in VPA). To the authors´ knowledge, in only one published study exercise intensity has been measured relative to cardiorespiratory fitness when riding an E-bike and a conventional bicycle. Gojanovic et al. [19] observed 55% of \( \overset{.}{\mathrm{V}}{\mathrm{O}}_2 \max \) when subjects cycled on an E-bike, and 72% of \( \overset{.}{\mathrm{V}}{\mathrm{O}}_2 \max \) during conventional bicycling, and slightly higher compared to the 51 and 58% in present study. In the present study, when the participants cycled on the conventional bicycle, the difference between the hilly and flat route was larger, probably due to higher physical effort cycling uphill without electrical support. Therefore, the findings may suggest that conventional bicycles are more sensitive to individual- and environmental factors, such as topography. Compared to studies on conventional bicycles, Oja and colleagues [32] supported the present findings, in 68 commuting adults, as the relative intensity was 57–65% of \( \overset{.}{\mathrm{V}}{\mathrm{O}}_2 \max \), whereas Geus et al. [17] observed a higher intensity of 77–79% of \( \overset{.}{\mathrm{V}}{\mathrm{O}}_2 \max \).

Exercise intensity, presented as METs, was in the present study also lower when subjects cycled on the E-bike compared to the conventional bike, however, figures for the hilly and flat routes were similar. The explanation for similar average MET-values during the flat and hilly routes are the periods of downhill with lower energy demand following the periods of ascending during hilly biking. A few previous studies have presented MET-values (4–6 METs) for E-bikes when cycling on a varied terrain [19–22]. These findings were similar, or somewhat lower, to the estimated METs in the present study, however, considerable lower than the measured METs. Presenting energy expenditure or exercise intensity using the standard 1-MET value (3.5 ml O₂/kg/min) may result in lower reported levels in individuals since the standard 1-MET value has been reported to be overestimating resting metabolic rate by 35 and 14% in individuals with a mean BMI of 30 and 20 kg/m², [25], respectively, and similar to the present study (resting metabolic rate of 3.0 ml O₂/kg/min). However, our results indicate that both using the standard 1-MET or measured RMR, e-biking can be categorised as at least MVPA.

E-biking was faster and less intense, making it suited for busy modern lives. It will get you quicker to work and you might not need a shower. But, on the other hand, less time spent cycling at a lower intensity is not ideal as most people are inactive. However, most of the time spent cycling on both the E-bike and the conventional bicycle, in both routes, was spent in MVPA.

The present findings indicate that due to lower intensity and trip duration, an E-bike needs to be used more frequently or to cover longer distances, to achieve the same health benefits [15], as adults commuting by a conventional bicycle. On the other hand, in several European nations, most adults do commute by motorised transportation to work [33], which according to Costa et al. [18] can be categorised as sedentary behaviour or light intensity physical activity (below 3 METs). Since the present findings indicate at least a moderate intensity of physical activity when e-biking, an increase in the level of transport-related physical activity will follow switching from car commuting to E-bikes, and more individuals probably meeting the physical activity recommendations. Also, considering that frequently reported barriers to cycling or walking for transport have been travel time [34–37] and physical effort [36, 37]; the E-bike seems to be a good option for those living too far away from work to walk or cycle with a conventional bike.