Part II: Intervals
Introduction
As identified in part I of this series of posts, the first decision I make when planning an indoor cycling class is whether it is going to be an interval-based or continuous session. In this second post of the series, I will discuss the further decisions I make if I opt for an interval-based session. As mentioned in part I, these decisions will be discussed in the context of indoor cycling classes in a health and fitness setting.
An interval-based session consists of periods of high intensity work interspersed with periods of rest, with the ratio of work-to-rest dependent upon the aim of the session. However, with participants in a health and fitness setting use of the strict work-to-rest ratios often cited for use with athletes may not be appropriate (see part I). Nonetheless, consideration should still be given to the intensity and duration of the work and rest periods. Additionally, the cycling position to be used during the work periods should be considered, as should the use of variations to standard intervals.
Intensity and work period duration
The intensity in an indoor cycling class is determined by a combination of cadence (leg speed) and resistance (as applied to the flywheel of the bike). A slow cadence with a low resistance will result in a low intensity, whilst higher intensities can be achieved with a faster cadence, a higher resistance, or a combination of the two. As resistance increases, the effort needed to achieve fast cadences increases, with attempts to generate a fast cadence against a very high resistance resulting in maximal intensity efforts.
As intensity increases, the duration for which it can be maintained decreases. For example, maximal intensity efforts can typically be maintained for no longer than a few seconds, whilst low intensity efforts may be maintained for several hours. This inverse relationship provides a basis for making decisions about the intensity and duration of work periods in an interval-based session.
In my interval-based sessions I generally use work period durations ranging from 10 seconds to 5 minutes. For planning purposes, work periods of 1 minute or less are termed short intervals, work periods of between 1 and 3 minutes are termed medium intervals, and work periods over 3 minutes are termed long intervals. If I have opted for an interval-based session, my next decision will be whether the session is going to consist of short, medium, or long intervals.
Having decided on the interval duration, the resistance to be used is considered. In the absence of a consistent way to apply resistance on the bikes I use (the mechanism for applying resistance can be affected by usage levels), I opt for terminology that describes how the resistance should feel. The terms that I typically use are “flat”, “small hill”, “big hill”, and “very big hill”; these terms approximately equate to moderate, moderate to heavy, heavy, and very heavy resistance respectively. Participants establish their resistances by progressing through lighter resistances during the warm-up until they have a moderate resistance on the flywheel (where any further increase would begin to feel like climbing a “small hill”). This moderate resistance is then their “flat”, and provides a basis for establishing the remaining resistances. The use of terminology such as “flat”, “small hill” etc. accounts for any differences between bikes, and helps to keep the intensity relative to each participant’s ability.
For short intervals, particularly those of 30 seconds or less, I will use higher resistances (i.e., “big hill” or “very big hill”), with the aim to generate fast cadences against these higher resistances. With such short durations, the high intensity should come from this combination of cadence and resistance. In my experience, trying to achieve higher intensities during short intervals using cadence with lower resistances does not elicit the required intensity, as participants reach and maintain a fast cadence relatively easily. Additionally, using fast cadences without enough resistance can result in excessively high leg speeds without sufficient control, thus increasing the chances of injury.
If using medium or long intervals, the desired intensity can be achieved via a combination of cadence and resistance. For example, if using a medium interval of 3 minutes with “flat” resistance, the intensity will primarily be achieved by maintaining a fast cadence for the duration of the interval. In contrast, if the same duration is used but with “big hill” resistance, then the intensity will primarily result from the resistance, as a fast cadence is not expected (participants should not be able to maintain faster cadences against higher resistances for such a duration).
Rest period duration
Following decisions about intensity and work period duration, rest periods need to be considered. As previously discussed, strict application of work-to-rest ratios is not always suitable in the health and fitness setting, as they can result in seemingly long rest periods (see part I). For example, text books suggest that a short, maximal effort interval (e.g., 10 seconds with “very big hill” resistance) requires a rest periods of at least 12 times the duration of the work period (e.g., 120 seconds), and a long interval of 5 minutes requires a rest period equal to the duration of the work period (i.e., 5 minutes).
To address these seemingly long rest periods, I would typically use a reduced rest period of 60 seconds for the short interval, and a reduced rest period of approximately 2 minutes for the long interval. During rest periods participants are encouraged to try and maximise their recovery by adopting a comfortable position of their choice (e.g., seated or standing), and reducing cadence and resistance. Additionally, participants are informed that they should be able to almost fully recover in the time available; however, it must be noted that compared to when using text book work-to-rest ratios, this will result in reduced intensity during work periods in order to allow recovery to occur. Consequently, different physiological responses and adaptations compared to when using text book work-to-rest ratios should be expected. In addition to information about the rest period, participants should be informed of the number of intervals to be performed; alongside information about the rest period duration, this allows them to make decisions about how to pace the intervals.
Despite not necessarily being appropriate for the health and fitness setting, with regular participants I do occasionally use the longer rest periods that result from strict application of text book work-to-rest ratios. Due to the time spent working with regular participants I feel that I can communicate the purpose of these work-to-rest ratios more effectively, and that participants have developed an understanding of their application to an interval-based session.
Cycling position
Further to decisions about intensity and work and rest period durations, I consider cycling position. Over the years I have been teaching indoor cycling classes I have narrowed the position options to seated or standing. Whilst other instructors use several variations on these positions, I only instruct participants to sit or stand. Providing participants are comfortable, and can achieve the required intensity safely, no further instructions are given. Limiting the position options and variations is based on feedback from regular participants, many of whom take part in other forms of cycling (e.g., road, mountain). These participants often indicate a preference for positions that replicate (as closely as possible) scenarios encountered on a real bike, and are not in favour of positions that would not be used when cycling outdoors.
The position I choose for an interval depends upon the interval duration and the resistance to be used. Standing or seated are used for short intervals using higher resistances, with seated the preferred option for medium or long intervals. In addition to specifying a position to be used for the duration of an interval, altering the position to be used within an interval is an option. For example, for short intervals with higher resistances, I might use a period of standing at the start of the interval to assist with overcoming the initial resistance, before switching to a seated position for the remainder of the interval. For medium and long intervals, I may provide a standing section at set points during the interval (e.g., the first 15 seconds of each minute) to allow a change of position for comfort, or to use body weight during the stand to maintain or regain cadence.
As well as specifying positions to be used during intervals, I also use intervals where participants have the option regarding the position they use. For instance, an option can be applied to short intervals with higher resistances (e.g., standing as an option during the first 15 seconds of a 60 second interval to help overcome initial resistance). Providing participants with an option also suits long intervals using higher resistances. These intervals can be considered “climbs”, with the aim to maintain as fast a cadence as possible throughout the interval despite the resistance. For such intervals I will often allow participants to choose their own position, and to switch between positions throughout the interval. This allows participants to adopt an approach that hopefully enables them to keep their cadence as fast as possible. Additionally, this lets participants who have their own approaches to climbing (based on experience of other forms of cycling) to apply them to indoor cycling.
Variations to standard intervals
Having considered intensity, work and rest period durations, and cycling position, what I term standard intervals can be implemented. Such intervals will begin with a countdown of “Ready, 3, 2. 1, Go!” or similar, with the clock starting on “Go!”. However, overcoming the initial resistance on the flywheel for short duration intervals using higher resistances can take time, meaning that a proportion of the interval is used to get up to speed. Whilst this is not necessarily an issue (participants still have to work at high intensities to overcome the initial resistance), it has led to me coming up with a couple of alternatives.
The first alternative is the “flying start”. The “flying start” allows participants up to 10 seconds to overcome the initial resistance and get up to speed before the interval starts. An option to stand during this period can be included before moving to a seated position for the interval. The second alternative is what I call a “wind up” interval. I typically use this alternative with 60 second intervals, and it involves starting at a slow cadence, and then increasing the cadence over the course of the interval, culminating in top speed being achieved for the final 10 seconds. Increases in cadence should be gradual, and participants should not have to make a big acceleration to hit top speed for the final 10 seconds. The increases in cadence can be every 10 to 15 seconds; however, for more experienced participants I allow them to make their own gradual increases in cadence providing they reach their top speed with 10 seconds to go. I do not use these alternatives with lower resistances, as there is less initial resistance to overcome, meaning that fast cadences can be achieved more easily and in a relatively short period of time compared to when using higher resistances.
Summary
Despite strict adherence to text book work-to-rest ratios not always being applicable in the health and fitness setting, if an interval-based session is chosen, intensity, work and rest period durations, and cycling position should still be considered. Including variations to standard intervals should also be given consideration. In part III of this series I will discuss continuous sessions as an alternative to the interval-based approach.
Paul Robertson, PhD 
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