Cycling research. High intensity interval training.

I took part in a cycling research study last year in April / May. It was led by Arthur Bossi who is a PHD student at the University of Kent. Arthur’s research was investigating intra – subject variability in acute physiological responses to high intensity interval training sessions. Arthur was easy to get on with and a great coach. I enjoyed the experience. Everything I took part in was at the University of Kent, Centre of Excellence for Sports Science Research at Medway Park.

My participation started with a ramp test and was followed by four high intensity training sessions. Ramp tests are typically used to assess VO2 max and ventilatory thresholds.

VO2 max is the maximum rate of oxygen uptake your body can achieve during exercise. It reflects your aerobic fitness, and it is an important determinant of your endurance capacity during prolonged exercise (≥ 5 min). VO2 max is mainly determined by the ability of your heart to pump blood through your body.

The Ramp Test

cycling research

Yellow: power output (W)  | Red: heart rate (bpm) | Green: cadence (rpm)

Ramp test results

Peak power output:324 W or 4.23 W.kg -1
Peak heart rate: 162 bpm
Mean cadence:92 rpm
VO2max :46.9 ml.kg -1 .min -1
GET:217 W (bottom dashed line)
RCP:279 W (top dashed line)

The gas exchange threshold (GET) and the respiratory compensation point (RCP) are also known as the first and second ventilatory thresholds. Both indices reflect the oxidative capacity of the skeletal muscle, and they are intimately related to the increases in blood lactate concentration during a ramp test. Often, they are used to prescribe training zones.

Zone 1 (<GET) is commonly used during low-intensity training sessions. Typically, continuous sessions are prescribed from 1 to several hours, depending on whether the aim of the session is an active recovery or an increase in endurance.

Zone 2 (between GET and RCP) is commonly used during moderate-intensity training sessions. Typically, continuous sessions are prescribed from 1 to 3-4 h, sometimes involving recovery breaks at Zone 1, with the aim of an increase in the oxidative capacity of the muscles.

Zone 3 (> RCP) is commonly used during high-intensity training sessions. Typically, interval-training sessions are prescribed with the aim of an increase in VO2 max and anaerobic capacity.

Reference values

Performance
Level:
VO 2max
(ml.kg -1 .min -1 )
Peak Power
Output (W.kg -1 )
Untrained< 45< 4.1
Recreationally trained45 – 54.94.1 – 5.0
Trained55 – 64.95.1 – 6.0
Well trained65 – 716.1 – 6.9
Professional> 71> 6.9

The high intensity interval training sessions

The structure of the training sessions and accumulated work duration at high intensity are generally prescribed according to the individual cyclist’s racing targets, performance limiters and periodization phase. Periodization generally follows a pattern in which training session goals gradually progress from Zone 1 to Zone 3 as the cyclists approach their main races of the season.

For me this meant each of the following four sessions started off with a 21 minute warm up of three 7 minute gentle intervals of incrementally increasing effort (130w, 152w, 154w). Then two minutes spin followed by four minute intense effort intervals at 281 watts, two minutes recovery and repeat until exhaustion. Recover from that and then a warm down with a repeat of the three 7 minute gentle intervals completed at the beginning of the session.

1st High-intensity interval training session [target: 281 W]

In the first session I managed three full intervals and about a minute and an half of the fourth.

cycling research

Yellow: power output (W)  | Red: heart rate (bpm) | Green: cadence (rpm)

GET: 217 W (bottom dashed line)  | RCP: 279 W (top dashed line)

1st High-intensity interval training session results

Time to exhaustion:19 min 28 s
Peak heart rate:168 bpm
VO2 peak :54.9 ml.kg -1 .min -1
Time ≥90% VO2 max :750 s
GE 1 :18.5%
GE 2 :19.3%
GE 3 :19.4%

2nd High-intensity interval training session [target: 281 W] 

This session I again managed three full intense intervals and about a minute and an half of the fourth. 

cycling research

Yellow: power output (W)  | Red: heart rate (bpm) | Green: cadence (rpm)

GET: 217 W (bottom dashed line)  | RCP: 279 W (top dashed line)

2nd High-intensity interval training session results

Time to exhaustion:19 min 36 s
Peak heart rate:170 bpm
VO2 peak :53.6 ml.kg -1 .min -1
Time ≥90% VO2 max :740 s
GE 1 :18.7%
GE 2 :18.8%
GE 3 :18.6%

3rd High-intensity interval training session [target: 281 W]

Bit better this time. Three full intense intervals and two minutes of the fourth. 30 seconds longer than best effort up till now. The virtual distance of each session was around 70km. 

cycling research

Yellow: power output (W)  | Red: heart rate (bpm) | Green: cadence (rpm)

GET: 217 W (bottom dashed line)  | RCP: 279 W (top dashed line)

3rd High-intensity interval training session results

Time to exhaustion:20 min 20 s
Peak heart rate:171 bpm
VO2 peak :54.3 ml.kg -1 .min -1
Time ≥90% VO2 max :790 s
GE 1 :18.5%
GE 2 :18.5%
GE 3 :18.9%

4th High-intensity interval training session [target: 281 W]

The last session. A bit better again. I managed three full intense intervals and two minutes and bit of the fourth.

cycling research

Yellow: power output (W)  | Red: heart rate (bpm) | Green: cadence (rpm)

GET: 217 W (bottom dashed line)  | RCP: 279 W (top dashed line)

4th High-intensity interval training session results

Time to exhaustion:20 min 10 s
Peak heart rate:168 bpm
VO2 peak :52.2 ml.kg -1 .min -1
Time ≥90% VO2 max :720 s
GE 1 :19.7%
GE 2 :20.0%
GE 3 :20.5%

The coaching guidance

High-intensity interval training sessions represent an important component of the training programme of every endurance athlete. You cannot realise your potential as a cyclist if you only perform continuous sessions at low to moderate intensities (< RCP).

In order to tax your body’s capacity for adaptation, you definitely need training sessions that demand maximal efforts performed to exhaustion such as the sessions you did in this study (> RCP).

Training sessions with large proportions of time spent at a high fraction of VO 2max (≥ 90% VO2 max ) are generally the most effective for improving VO 2max and performance due to the greatest training stimulus. However, the prescription of optimal interval-training sessions is not simple.

Instead of 2 components influencing the acute physiological responses (i.e. intensity and duration, in the case of continuous exercise), at least 5 major components need to be considered in the case of interval training: (1) the duration of the session (i.e. the number of intervals), (2) the duration of the work interval, (3) the duration of the recovery interval, (4) the intensity of the work interval and (5) the intensity of the recovery interval.

This study has been conducted in order to optimise the prescription of the 4th component. As you now appreciate, time to exhaustion and time ≥90% VO2 max vary quite a bit from one session to another. It means that you should always perform these sessions until the point of exhaustion, which is the point where you cannot keep the target power output.

In order to increase time ≥90% VO2 max, a good strategy might be to lengthen the standard recovery interval (for example 2.5 instead of 2 min) to allow at least 4 or 5 full work intervals before you reach exhaustion. Alternatively, you can lengthen the recovery interval only after you reach exhaustion,therefore allowing you to perform a few more work intervals before quitting.

If you prefer to do these intervals outdoors, find a quiet stretch of road and aim to keep the power output ± 15 W around your target intensity. In case you do not have a power meter you can try to simulate the sessions you did in the lab if you observe the behaviour of your heart rate in relation to power output carefully. By monitoring the distance covered, you can have a good estimation of your ability to produce similar average power outputs in each 4- min work interval, allowing you to decide when a slightly longer recovery interval is necessary.

Some athletes have been able to perform more than 6 work intervals before reaching exhaustion. This is actually the reason I am doing this PhD, as “individualised” intensity prescriptions do not really standardise performance and the physiological responses across different athletes. If you are one of those that did more than 6 intervals, you might benefit from slightly higher power outputs than in the present study. Increasing the target intensity by 5-10 W might be an effective strategy to increase the training stimulus without shortening the time to exhaustion too much. The same is true if you observe that time to exhaustion tended to
increase during the study or if you reached VO2 peak values higher than VO2 max.

Gross efficiency (GE) is the ratio between external work (which depends on your power output) and metabolic energy demand (which depends on your oxygen uptake). As you now appreciate, only about 20% of your energy demand is converted into external work, the remainder being lost as heat. Although GE is pretty much stable across different individuals, there is some evidence that it can increase slightly with high volumes of training and especially after high-intensity interval training programmes, increasing your ability to produce external work from a particular energy requirement.

Generally, GE values higher than 20% are found in the best athletes. Although this study was too short to cause changes in GE, if you have already improved, there is one more reason to include high-intensity interval training in your weekly routine. We measured GE during three different workloads in order to provide a better representation of your physiology. Observe the trends instead of focusing on a single number.

The takeaway.

I have a reasonable baseline fitness with potential and ability to improve. By sticking with what I am doing I shall maintain this good enough level of fitness for the foreseeable future. Good enough will do. Improvement is a lot of hard work. Taking part in this cycling research was as hard as I was led to believe. Pushing myself to the limit in this way is not for me. Long distances cycling is a much more enjoyable route to exhaustion, at least in my book anyway. It was an interesting experience and fun to be involved but once is enough. I like being outside, exploring on my bike and riding at a comfortable pace. I shall leave training indoors and fast riding to the roadies and circuit racers. Hats off to you all. 

An opportunity to get involved

If you are one of those I have just described and getting fed up with the cold winter weather, live in or close to Kent and want to keep training at a high level you might enjoy taking part in Arthur’s current research project – 

cycling research

If you do fancy benefiting from and helping out with cycling research get in touch with Arthur and give him my best.