This post summarises the findings of testing I conducted to quantify the effect of using a hiking trailer to transport a backpack in comparison to carrying that backpack. Effects on energy usage, walking speed and heart rate were checked. In particular, the testing was intended to answer the question: does using a hiking trailer save you energy?

The paper describing the testing in full is available from here.

The study does not claim to represent independent testing. All testing and analysis was done by the inventor of the Trekker’s Friend hiking trailer. This may introduce a degree of bias.

The findings reported here are not commercial claims for the Trekker’s Friend. Anyone purchasing or using the device will need to perform their own testing to establish whether it fulfils their requirements.

Nonetheless, this testing presented a significant effort to understand whether using a hiking trailer will save you energy. Detailed results of the testing can be provided on request.

## Summary of testing and findings

A series of 54 test walks were taken around a level, sealed, 7.12 km circuit between April and August 2018. Six trials each time were done walking without a backpack, carrying a backpack, and taking the backpack on the Trekker’s Friend hiking trailer, with backpacks weighing 10 kg, 15 kg, 20 kg and 25 kg.

The study found that:

- Using the trailer to transport a backpack consumed from 42.9% to 69.9% less energy per km than carrying it (not including the energy used just for walking)
- Using the trailer consumed from 3.7% to 13.7% less total energy (i.e. including energy required for walking) per km than carrying the backpack
- Although the test subject’s heart rate was higher when walking with a backpack than without, there was no statistically significant difference in heart rate between carrying the backpack and using the trailer
- The test subject walked from 5% to 11% faster when using the trailer than when carrying the backpack
- The greater the weight of the backpack, the greater the difference in total energy consumption and walking speed between using the trailer and carrying the backpack.

In summary, yes, in comparison to carrying your backpack, using a hiking trailer will save you energy. It will also allow you to walk faster at the same time.

## Methodology

A series of test walks were conducted for each of the following modes of travel:

- No load (and no trekking poles)
- Carrying a pack (with no trekking poles)
- Pulling a pack along with the Trekker’s Friend hiking trailer.

Four different load weights were tested with both the walking trailer and carrying the pack: 10 kg, 15 kg, 20 kg and 25 kg. These weights refer to the weight of the backpack only. When the backpack was being carried, neither the Trekker’s Friend nor the poles were taken on the test circuit. When the backpack was wheeled, the weight of the Trekker’s Friend and trekking poles was not counted in the total weight.

Six repetitions were done for each mode of travel, and for each of four weights when taking the pack. This means a total of 54 test walks were conducted (6 with no load, 24 carrying the backpack, and 24 pulling the backpack), producing 54 sets of measurements.

The walking circuit used for all test walks was the bike path around Lake Ginninderra in Belconnen, Canberra, Australia, as shown below. The course has an average altitude of 587 m, which varied by a total of 16 meters over the course of 7.12 km.

The three main variables that were measured were:

- Energy expenditure – in kilocalories (kcal)
- Walking Speed – in kilometres per hour (km/h)
- Heart rate – in beats per minute (bpm).

These variables were measured with a Suunto Ambit Run GPS watch and heart monitor, both of which were worn by the test subject for each test walk.

The test subject noted the cumulative energy expenditure at three milestones along the way (at 2.18 km, 3.47 km and 5.98 km) and at the end of the circuit.

The circuit was walked no more than once per day, at approximately the same time of day – after breakfast, at some time between 7am and 10am, and the test subject traversed the circuit in the same direction for every test walk.

## Analysis of results

The results were analysed in the following way:

- At the end of each test walk the test subject entered walking speed, heart rate and total energy consumption, along with the energy consumption at the three intermediate milestones, into an Excel spreadsheet
- Energy expenditure per kilometre (kcal/km) was calculated
- The amount of energy required solely to transport the backpack was calculated by subtracting the total amount of energy used when walking without a backpack from the total amount of energy used when walking with the pack
- The amount of energy required to transport the pack by carrying it was compared to the amount of energy required to transport it with the walking trailer, for each weight
- Statistical tests were conducted using the 0.05 significance level to determine whether the differences in readings when using the hiking trailer (compared to carrying the backpack) were statistically significant.

If a difference is said to be “statistically significant” it means that it is reasonable to have a given level of confidence that the difference is not simply due to chance. In this paper, “T-tests” were performed using the 0.05 significance level to provide a 95% level of confidence that the differences between the samples was not due to chance.

## Results

### Walking speed

Differences in average walking speed according to the mode of travel (over the course of the 7.12 km track) are shown in Figure 1 and indicate that:

- With no load, the average walking speed was 5.7 km/h
- The test subject walked more slowly when carrying the pack than without one, and their speed decreased as the pack’s weight increased, especially with the 25 kg pack
- The test subject walked significantly faster when using the walking trailer than when carrying the pack, and this was true for all load weights.
- When pulling the pack, walking speed did not vary as much with weight increases as for when carrying the pack
- The average speed when pulling the pack was slightly faster than when walking without a load – for all weights except 25 kg.

Table 1 below shows the relative increase in walking speed when using the walking trailer compared to carrying the pack. These results indicated that:

- The differences in walking speed according to whether the pack was carried or pulled on the trailer were statistically significant, for all load weights
- The improvement in walking speed when using the walking trailer (compared to carrying the pack) became greater as the load increased – from 5.1% with 10 kg to 11.0% with 25 kg.

Weight of pack | Speed carrying pack (km/h) | Speed using trailer (km/h) | Increase in speed with trailer (km/h) | Increase in speed with trailer (%) | Statistical Significance |

10 kg | 5.5 | 5.8 | 0.3 | 5.1% | IS SIGNIFICANT |

15 kg | 5.5 | 5.9 | 0.5 | 8.2% | IS SIGNIFICANT |

20 kg | 5.4 | 5.8 | 0.4 | 7.5% | IS SIGNIFICANT |

25 kg | 5.0 | 5.5 | 0.5 | 11.0% | IS SIGNIFICANT |

**Table 1: Walking speed**

In summary, this study found that, on a level sealed track, using a hiking trailer to transport your backpack will allow you walk faster than if you carry your backpack, and this effect increases the heavier your backpack is.

### Heart rate

As shown in Figure 2 below, the test subject’s average heart rate:

- Was 94.2 bpm when walking with no load
- Increased slightly when walking with packs of all weights, compared to walking without one
- Did not differ much according to whether the pack was carried or pulled with load weights from 10 kg to 20 kg
- Increased the most when the 25 kg pack was carried compared to being pulled.

Table 2 below shows the relative reduction in heart rate when using the walking trailer compared to carrying the pack. These results indicated that:

- The differences in heart rate according to whether the pack was carried or pulled on the trailer were very small and not statistically significant, for any load weight.

Weight of pack | Heart rate carrying pack (bpm) | Heart rate pulling pack on trailer (bpm) | Reduction in heart rate with trailer (bpm) | Reduction in heart rate with trailer (%) | Statistical Significance |

10 kg | 97.0 | 97.5 | -0.5 | -0.5% | NOT SIGNIFICANT |

15 kg | 97.5 | 97.7 | -0.2 | -0.2% | NOT SIGNIFICANT |

20 kg | 97.7 | 97.2 | 0.5 | 0.5% | NOT SIGNIFICANT |

25 kg | 102.2 | 99.5 | 2.7 | 2.6% | NOT SIGNIFICANT |

**Table 2: Heart rate**

In summary, this study found that, on a level sealed track, using a hiking trailer to transport your backpack does not significantly change your heart rate compared to carrying your backpack.

## Total Energy Consumption, Per Kilometre

The total energy consumption per kilometre was calculated by dividing the total energy consumption by the number of kilometres in the test circuit. Total energy consumption per kilometre for each mode of travel and load weight is illustrated in Figure 3 below, which shows that:

- Traversing the test circuit without a pack consumed 65.7 kcal/km on average
- Walking with a pack consumed more energy per km than walking without one, for all load weights
- Carrying the pack consumed more energy per km than while pulling the pack on the trailer, for all load weights.

Table 3 below demonstrates how much of the total energy consumed when carrying the pack is saved when pulling the pack with the Trekker’s Friend trailer. The results show that:

- The relative energy savings per kilometre when using the trailer increased as the load weight increased, from 3.7% with 10 kg to 13.7% with 25 kg
- The difference in total energy consumption per kilometre between carrying the pack and pulling it on the trailer was statistically significant for every weight except 10 kg.

Weight of pack | Total energy carrying pack (kcal/km) | Total energy with trailer (kcal/km) | Reduction in total energy with trailer (kcal/km) | Energy (kcal/km) reduction with trailer (%) | Statistical significance |

10 kg | 71.8 | 69.2 | 2.6 | 3.7% | NOT SIGNIFICANT |

15 kg | 73.5 | 68.0 | 5.5 | 7.5% | IS SIGNIFICANT |

20 kg | 75.5 | 69.3 | 6.2 | 8.2% | IS SIGNIFICANT |

25 kg | 88.2 | 76.1 | 12.1 | 13.7% | IS SIGNIFICANT |

**Table 3: Reduction in total energy consumption per kilometre**

In summary, in regard to total energy used, this study found that, on a level sealed track, using a hiking trailer to transport your backpack will save you energy per km compared to carrying your backpack, and this effect increases the heavier your backpack is.

## Energy Consumed Solely to Transport the Pack, Per Kilometre

The amount of energy consumed solely to transport the backpack does not include the energy required for walking. It was calculated by subtracting the total amount of energy used when walking without a pack from the total amount of energy used when walking with the pack.

Energy consumption solely to transport the pack, per kilometre, for each mode of travel and load weight is illustrated in Figure 4 below, which shows that:

- Carrying the backpack consumed more energy solely to transport the backpack per km than while pulling the pack on the trailer, for all load weights.

Table 4 below demonstrates how much of the energy consumed solely to transport the backpack when carrying the backpack is saved when pulling the pack with the *Trekker’s Friend* trailer. The results show that:

- The savings in energy solely used to transport the pack per kilometre when using the trailer rather than carrying the pack ranged from 42.9% to 69.9%.

Statistical significance was not calculated as these are derived values.

Weight of backpack | Carrying backpack (kcal/km) | Backpack on walking trailer (kcal/km) | Reduction in energy use per km solely to transport pack with trailer (kcal/km) | Reduction in energy use per km solely to transport pack with trailer (%) |

10 kg | 6.1 | 3.5 | 2.6 | 42.9% |

15 kg | 7.9 | 2.4 | 5.5 | 69.9% |

20 kg | 9.8 | 3.6 | 6.2 | 63.2% |

25 kg | 22.6 | 10.4 | 12.1 | 53.7% |

**Table 4: Reduction in energy consumed solely to transport the pack, per kilometre**

In summary, in regard to energy used just to transport your pack (ie. with the energy used just to walk subtracted from total energy used), this study found that, on a level sealed track, using a hiking trailer to transport your backpack will save you energy per km compared to carrying your backpack, and this effect increases the heavier your backpack is.

## Total Energy Consumption at Milestones

Energy consumption readings were taken at three milestones while walking the test circuit and at the conclusion of each walk. See the paper itself for detailed information on this area.

In summary, the milestone readings showed that energy was consumed at a steady rate throughout the course of the walk and that similar differences were seen throughout the test circuit – ie. the advantages provided by using a hiking trailer did not change over the distance, and were statistically significant throughout the test distance.

## Summary of Results

This study examined three key measures relating to the effort required to transport a pack by carrying it compared to pulling it on the Trekker’s Friend trailer – speed of walking, heart rate, and energy consumed over the 7.12 km course. It then derived the energy consumed per per km from this information. It found that:

- The test subject walked from 5% to 11% faster when using the trailer than when carrying the pack, and the increase in speed was statistically significant for all load weights

- The test subject’s heart rate did not differ in a statistically significant way for any transport method for any load weight

- Using the trailer to transport the pack around the test circuit consumed from 3.7% (for a 10 kg pack weight) to 13.7% (for a 25 kg pack weight) less total energy per km than carrying the pack and the difference was statistically significant for all but the lowest load weight

- The energy used solely to transport the pack (not including the energy used just for walking) on the walking trailer was 42.9% to 69.9% less per km than carrying it

- Differences in energy consumption that were statistically significant for the circuit as a whole, were of a similar magnitude throughout the walking circuit. When these differences were statistically for the entire circuit, they were also statistically significant at all milestones in the circuit.

The comparisons between carrying a pack and using the Trekker’s Friend walking trailer are summarised in Table 6 below, with statistically significant findings **bolded**, where relevant:

Weight of pack | Increase in walking speed with trailer | Reduction in heart rate with trailer | Reduction in total energy use per km with trailer | Reduction in energy use per km solely to transport pack with trailer (statistical significance not relevant) |

10 kg | 5.1% | -0.5% | 3.7% | 42.9% |

15 kg | 8.2% | -0.2% | 7.5%, | 69.9% |

20 kg | 7.5% | 0.5% | 8.2% | 63.2% |

25 kg | 11.0% | 2.6% | 13.7% | 53.7% |

**Table 6: Summary of results on energy consumption and walking speed**

In summary, this study found that the effects reported above

## DISCUSSION

**Effects of Walking Trailer on Energy Consumption, Walking Speed and Heart Rate**

The main purpose of this study was to investigate whether using the Trekker’s Friend hiking trailer reduced the effort required to take a pack when walking. It was expected that wheeling the pack on a trailer would use less energy than carrying it, which was found to be the case. However, the magnitude of the energy savings was unexpected. The study found that using the Trekker’s Friend trailer to transport a pack used up to 69% less energy per kilometre solely to transport the load than was required for carrying the pack.

The study found that when using the trailer, the subject walked 5-11% faster than when carrying the pack (depending on the pack weight). The increase in speed was found to be statistically significant. At the same time, the heart rate remained about the same, whether carrying the pack or using the trailer. Finally, the test subject used 3.7-13.7% less total energy per km through using the trailer while walking faster.

Together, these findings suggest that the test subject adjusted their speed of walking to maintain about the same rate of energy consumption, which is why their heart rate remained the same. Using the walking trailer was an easier way to transport the load over any given distance, which is why, overall, they walked faster and used less energy per km while doing so.

**Other relevant research**

Several researchers have developed equations to predict energy expenditure while walking (Ludlow and Weyand, 2016). While these equations vary, they all show a direct relationship between walking speed and energy expenditure. Hutchison (2018) notes that the equation developed by Pandolf “has been used since the 1970s to estimate how much energy it takes to hump a pack”. This equation predicts that:

- As the weight of the pack increases, energy consumption per km also increases
- As the speed of walking increases (above a slow walk of 3.2 km/h) the energy consumption per km increases.

For example, according to Pandolf’s equation:

- For a hiker weighing 100 kg (220 lbs), carrying a 25 kg (55 lbs) pack, with a hiking speed of 5.0 km/h (3.1 mph), with a slope of 0%, on a paved road, total energy consumption would be 146 kcal per 1.6 km (1 mile) / 91 kcal per km.
- If all variables remain the same but the hiking speed is increased to 5.5 km/h (3.4 mph), energy consumption should be increased to 151 kcal per 1.6 km (1 mile) / 94 kcal per km (ie. by 3.4%).

For the test walks when carrying the pack, the findings of this study were largely in accordance with those predicted by Pandolf’s equation. The test subject for this study weighs 100kg, and with the 25kg pack he walked at 5km/h. His total energy consumption was 88 kcal / km, which is similar to that predicted by Pandolf’s equation (see Table 3).

However, for the test walks using the Trekkers Friend trailer the results did not follow the predictions of Pandolf’s equation. When the test subject used the Trekkers Friend to pull a 25 kg pack instead of carrying it, the walking speed increased from 5.0 km/h to 5.5 km/h but energy consumption was reduced by 13.7% rather than being increased by 3.4% as would be predicted by Pandolf’s equation. The same effect is seen for other pack weights – ie. walking speed increased although energy consumption per km decreased (see Table 3).

As for the previous subsection, the most likely explanation for this is that since it is easier to pull the pack instead of carrying it, the subject is able to walk faster, while expending less energy per km. This suggests that if the walker had walked at the same speed when using the trailer as when carrying the pack, then the savings in energy consumption per km may have been even greater.

## REFERENCES

**Ludlow L, Weyand P (2016) **Energy expenditure during level human walking: seeking a simple and accurate predictive solution. J ApplPhysiol 120: 481–494, https://www.physiology.org/doi/pdf/10.1152/japplphysiol.00864.2015, viewed 28^{th} Aug 2018

**Hutchinson A** **(2018) **The ultimate backpacking calorie estimator. Outside Online, https://www.outsideonline.com/2315751/ultimate-backpacking-calorie-estimator, viewed 28^{th} Aug 2018.