Peak Performance looks at new research on the accuracy of maximum heart rate prediction formulae, and what this means for athletes who use heart rate monitoring to guide their training intensity MORE
Training plan: monitoring your training intensity
Quantifying the training load of athletes in the ever-faithful training diary has always been of great importance to coaches. But according to Alan Ruddock, without some kind of record of the body’s physiological response to exercise, it’s hard to really assess an athlete’s condition.
Alternatively, the coach may wish to know what type, intensity, duration and frequency of training stimulus is optimal to develop maximal aerobic capacity (VO2max). Using a past history of training load and physiological test results, it’s possible to determine how much training is required to improve VO2max. Successful monitoring and assessment of training may then lead to improvements in performance.
A number of methods to quantify ‘training load’ have been used for training and monitoring in different sports, including athlete self-assessment of training sessions, simple calculations of volume and heart rate (HR) response methods. The commonest method now used for monitoring training load is ‘Training Impulse’ or ‘TRIMP’, which was formulated by Bannister in 1975. Since Bannister first introduced the TRIMP it has been modified several times to refine its use of HR data.
Although HR monitoring is both valid and reliable, problems can occur when using this information to interpret physiological responses. For example, the relationship between HR and blood lactate is linear at low to moderate speeds/power outputs but as exercise intensity increases, HR increases linearly but blood lactate rises exponentially – ie the various physiological responses occur that are not necessarily reflected in HR data alone.
To overcome this problem, Carl Foster introduced a weighting category based upon percentages of maximum heart rate to give a TRIMP score. He also used perceived rating of exertion (PRE) to provide an overall subjective assessment of a training session (1). In a further development, a research group from Spain gave weightings to three physiological stages based upon analysis of inspired and expired oxygen and CO2 (2).
Following an incremental exercise test to exhaustion, an analysis of oxygen and CO2 gas flows in the body can reveal two distinctive changes in ventilation, which represent different physiological occurrences in response to an increase in exercise intensity (see figure 1):
- The first identifiable point is the ventilatory threshold (VT) – it represents one of the body’s initial responses to a change in homeostasis as a result of exercise;
- The second identifiable point is the respiratory compensation point (RCP), which marks the exercise intensity at which heavy breathing is required to help remove metabolites from the body.
The Spanish researchers tested eight national and regional level male runners to determine their VT and RCP. They then used the modified TRIMP to provide the following weighting factors.
Zone 1: Light intensity, heart rates below the exercise intensity that elicits VT; 1 minute of exercise in zone 1 is given a score of 1;
Zone 2: Moderate inensity, heart rates between the exercise intensity that elicits VT and RCP; 1 minute of exercise in zone 2 is given a score of 2;
Zone 3: High-intensity heart rates above the RCP; 1 minute of exercise in zone 3 is given a score of 3.
After determining the training zones the researchers gave HR monitors to all participants and asked them to wear the monitor each time they trained. The purpose of this was to determine the relationship between training load and running performance during the most important competitions of the season (ie national cross country championships). Training load was monitored each session over a six-month period.
Results showed that the athletes in this study spent most of their training time (71%) at low intensities (zone 1). The percentage of time training at moderate (zone 2) and high (zone 3) intensities was 21% and 8% respectively. In this particular group of athletes, there was a significant correlation between the amount of time they spent training in zone 1 and performance in both the short and long cross country races; the athletes who spent more time training at a low intensity (below VT) performed better in a high-intensity (30 minutes of continuous exercise in zone 3) race!
In another study, British scientists recognised that training at higher intensities should be awarded larger weighting factors because of the greater physiological demand imposed by high-intensity training (3). Using blood lactate and HR responses to a treadmill test and a concept known as the ‘fractional elevation’ in heart rate, they arrived at a five-zone system that more accurately reflects the increased physiological stress imposed by high-intensity activity (see table 1).
Similar to previous TRIMP methods, the total time spent in each zone was multiplied by a weighting factor to calculate training load. The difference in this instance is that as exercise intensity increases, the weighting factor increases exponentially rather than linearly. In previous TRIMP methods low (zone 1) intensity exercise was given a weighting of 1 and high (zone 3) intensity a weighting of 3, a simple linear increase. The five-zone method gives high-intensity activity a weighting about seven times greater than low-intensity activity.
The researchers who developed this method gave eight male premier league hockey players a HR monitor and recorded their HR responses to training and competition from the start to the middle of the season. They found that those players who had a higher mean weekly TRIMP value had the largest change in VO2max and velocity at OBLA, suggesting that the greater the training volume, the greater the increase in VO2max and velocity at OBLA.
The percentage changes in VO2max and velocity at OBLA were also correlated with the mean weekly time spent in high-intensity training (zones 4 and 5). This suggests that the more time spent training at a high intensity, the greater the improvements in VO2max and OBLA. Interestingly, the researchers calculated how much weekly TRIMP value players needed to accumulate to maintain VO2max and velocity at OBLA. They found that players needed a lower mean weekly TRIMP value to maintain VO2max than OBLA and needed to spend less time engaged in high-intensity training to maintain VO2max than OBLA.
These calculations are particularly useful to coaches when planning and monitoring training as they can ensure that each player is receiving a sufficient training stimulus to maintain or improve VO2max and OBLA throughout the season. The major limitation to this study is that it only took into account endurance training when hockey training most likely comprises of speed and strength training too.
Intermittent sports training
Most sports, especially team sports, comprise a mix of three basic physical qualities, speed, strength and endurance. However, previous TRIMP systems have been limited to identifying the training load of endurance training and have not been able to account for other training loads using one single TRIMP method.
French researchers attempted to quantify the training loads of endurance, sprint and strength training using one single TRIMP method for use with intermittent sports training(4). The Work Endurance Recovery (WER) method created by this team is based upon the theory that training-induced physical stress can by quantified in relation to an athlete’s maximal work capacity. So rather than training loads being quantified in relation to physiological responses (eg blood lactate, HR or VO2max and CO2), it is based on ‘fatigue occurrence’, making it possible to monitor different training load types using a single equation (see box 1).
The researchers above compared the WER method with TRIMP methods to determine how accurately they measured training loads by asking participants to exercise until exhaustion in three separate sessions – one endurance, one sprint and one strength. They then assumed that each session provided a similar training load – ie around 33% of total volume each and because the WER equation calculates training load in relation to fatigue; the total work capacity of 100% divided by three sessions equates to about 33%.
They discovered that there was no difference between the calculated training loads of sprint or strength training regardless of which TRIMP method used. However, large differences in training loads were observed between endurance training and sprint/strength training; endurance session training loads were 2.5-2.8 times higher than sprint training and 5.1-5.5 times higher than the strength training. This confirmed that the TRIMP methods are incompatible when comparing training loads of different exercise modes. By contrast, when they used WER, they found that each session represented around 31 -35% of the cumulated training load indicating that there was no difference between the training sessions and confirming the group’s hypothesis.
Despite some limitations relating to the determination of endurance limits, the major advantage of the WER method over TRIMP methods is that it allows the comparison of different training sessions on the same scale and is thus a good base for the development of monitoring training loads in intermittent sports.
If you want to calculate your TRIMP scores, choose a method most appropriate to your sport. For sports where you undertake only one type of training (eg running or cycling) then one of the TRIMP methods may be the most appropriate for you. The modified five-zone TRIMP is probably the best choice for monitoring training load in this instance because the test protocol and data analysis to determine the blood lactate curve is less complicated and time consuming than gas analysis used by the three-zone TRIMP. And while calculating the weighting factors using five-zone TRIMP is a little more complicated, these factors provide a far more accurate load calculation when exercise is intense.
If you participate in sports that requires a mix of two types of exercises or more such as track and field sprinting (which requires sprint training and weight training) or rugby (which requires endurance, sprint and weight training) then the WER method may be more appropriate for you. The testing can be conducted outside the lab, requires no sophisticated equipment and providing you follow the calculations accurately (it’s probably easiest if you use a spreadsheet) the WER method is a good option to monitor training load across different types of exercise.
Alan Ruddock MSc, CSCS, YCS is a researcher in exercise physiology at Sheffield Hallam University, UK
1. J Strength Cond Res, 2001, 15(1), 109 – 115
2. Med Sci Sports Exerc, 2005, 37(3), 496-504
3. J Sports Sci, 2007, 25(6): 629-634
4. Appl Physiol Nutr Metab, 2007, 32(4): 762-769