Thursday, 7 June 2012

1. Athletic track test of barefoot versus Hyperspeed

Comparison of physiological effort of running barefoot compared to Asics Hyperspeed

Summary

We examined physiological effort, using heart beats per km as an index, for two subjects (aged 14 & 45) running shod (~200g per shoe) and barefoot around an outdoor synthetic athletics track at ~4:30 min per km. Both runners showed a progressive rise in physiological effort during the first four shod runs. On running barefoot (for the first time) both runners showed a progressive decline in physiological effort which ceased on returning to the shod condition. The changes in physiological effort were ~2% and consistent with previous efficiency gains associated with lighter running shoes. However, no significance testing was performed, and this is just a preliminary study so conclusions must be limited. Nevertheless, it seems very unlikely that running barefoot is less efficient than shod on a synthetic athletics track.

Introduction

The idea we set-out to test is whether running barefoot or in lightweight running shoes results in the lowest amount of physiological effort. Whilst there have been many studies of barefoot running, almost all have been done on treadmills. Treadmills tend to be rather elastic and do not necessarily replicate the surface encountered in outdoor running. There has been a study of barefoot running on an indoor track - however, we have attempted here to get a little bit closer to normal, 'real-world' running.
The test surface was an outdoor athletics track (Cambridge University Athletics Track) which has a typical synthetic surface. The surface was selected as both participants (my son and I) had not engaged in barefoot running (except a few years ago on a beach...) and therefore required a consistent, mildly abrasive surface free of stones and other hazards.
The test was conducted at constant (but not controlled) pace wearing Garmin 305 GPS/heart rate monitors with which we assessed physiological effort. It is relatively well known that heart rate rises and falls as 'physiological effort' changes during running. As you run faster heart rate rises due to the greater supply of blood required by your muscles - equally as you slow down heart rate falls as your muscles demand less blood. Thus, during a run heart rate is a good indicator of changes in physiological effort (work being done). Of course there are other reasons why heart rate may change - dehydration and thermoregulation are good examples - but, such challenges tend to occur gradually. Thus, heart rate during an exercise session - once in steady-state - is a good indicator of physiological effort. By doing repeat measurements of speed and heart rate we have calculated the number of heart beats per km associated with barefoot and shod running.


Methods

We arrived at the athletics track around 7pm on an overcast day. The track was empty and free from distractions. We selected lane 8 (~450m) for our test, staying as close as possibly to the inner side of the lane. We had two subjects (Max, aged 14 and I, aged 45) and decided on a two lap (~900m) measurement for each test with an additional 100m flying-start. We used an alternating protocol to avoid distracting each other and influencing pace. Max first ran two laps, then on his last 100 m I joined in and started my two laps. On my last 100m Max joined in an started his next two laps - and so on. Thus, we ensured a constant rest between laps with minimal distractions. We decided upon four sets of two laps each in our normal running shoes, followed by three sets of two laps each barefoot and then another three sets of two laps back in the running shoes again. This produced 10 sets of data. Max and I ran mainly by feel, selecting a pace that was comfortable and sustainable. We did not attempt to match each others pace (except for the 100m flying start), or changes of pace during the sets. Average heart rate and time were collected from the watches and heart beats per km were calculated.

Results

Table 1 shows the data from all ten sets. Max and I ran at very similar speeds, between 4:39 and 4:31 per km, with a progressive speed increase between sets. Max's heart rate was also, on average, 38 beats per minute higher than mine - unsurprising given our age and training differences. I recently ran a 3:07 marathon and Max does no consistent running except for the occasional parkrun (5K). 

Runner
Set
Test
Time
Pace
HR
beats per km
Max
1
Shod
04:11
04:39
155
720
Max
2
Shod
04:10
04:38
164
759
Max
3
Shod
04:04
04:32
167
756
Max
4
Shod
04:07
04:34
171
781
Max
5
Barefoot
04:06
04:33
171
778
Max
6
Barefoot
04:07
04:34
169
772
Max
7
Barefoot
04:06
04:34
168
766
Max
8
Shod
04:02
04:29
169
758
Max
9
Shod
04:02
04:29
169
758
Max
10
Shod
04:04
04:31
169
764
Christof
1
Shod
04:10
04:38
123
567
Christof
2
Shod
04:12
04:40
127
592
Christof
3
Shod
04:11
04:39
128
595
Christof
4
Shod
04:09
04:36
132
608
Christof
5
Barefoot
04:08
04:36
133
611
Christof
6
Barefoot
04:07
04:34
131
599
Christof
7
Barefoot
04:05
04:32
131
595
Christof
8
Shod
04:06
04:33
129
586
Christof
9
Shod
04:05
04:32
130
589
Christof
10
Shod
04:05
04:32
130
589

Table 1. Data from each subject for the ten tests (in sequence: 4 shod, 3 barefoot, 3 shod).

In Figure 1 I have plotted the pace for each lap, and the gradual increase in speed is obvious. It is interesting to note that both Max and I gradually increased the speed by a similar amount without discussion or prior agreement - although, my pacing was generally more consistent than Max's. The barefoot condition (open symbols) was not associated with any obvious change in pacing. 
Figure 1. Plot of pace for each test (open symbols show the barefoot tests). Note the arbitrary y-axis limits selected to allow the progressive increase in pace to be seen. 
In Figure 2 the relative heart rate (relative to the average across all ten tests for each subject) is shown plotted. Both Max and I had very similar relative heart rate changes with an initial rise in heart rate over the first four tests, followed by a plateau or slight decline in heart rate during the barefoot running which was maintained on returning back to running shoes. However, the pace fluctuations may confound a simple heart rate analysis.
Figure 2. Plot of heart rate (relative to the average for each subject over the 10 tests). Again, arbitrary y-axis ranges were chosen. Open symbols show the barefoot tests. 
 A simple way method of correcting for pace variations is to calculate heart beats per km. These data are shown in Table 1. Max had a mean value of 761 heart beats per km, whilst mine was 593 heart beats per km. To allow a better comparison of Max and my data I have plotted the heart beats per km relative to these averages (Figure 3). This form of normalization removes the offsets and allows changes in physiological effort to be compared between different people.
Figure 3. Relative heart beats per km plotted against test number. The relative heart beats per km was calculated as the heart beats per km divided by the subject's average heart beat per km over the ten tests. This form of correction allows relative changes in efficiency to be seen without the offset due to differences in heart rate between individuals.
Both Max and I showed a progressive rise in the number of heart beats per km for the initial 4 tests. This type of initial rise is always seen during a warm-up period. The following three runs barefoot (open symbols) was associated with a modest decline in heart beats per km which appeared to reverse on returning to the shod condition.

Discussion

The initial four runs produced a progressive rise in heart beats per km (physiological effort) typical of these types of test. Interestingly the first run barefoot produced similar values as the previous shod run, and the two subsequent barefoot runs produced lower physiological efforts. This, ~2% decline during the barefoot tests, is consistent with barefoot running being more efficient and is a similar degree of efficiency gain previously seen with a reduction in running shoe weight. On returning to the running shoes for the final three tests, the progressive decline in effort seen during barefoot running appeared to reverse (although only partially) producing a very modest increase. The similarity between Max and my traces is striking despite having done the runs separately and without a prior pacing plan. The changes in the data between the shod and barefoot conditions are not sufficiently striking to be confident that other time dependent phenomena (including the pace variations) are not confounding the results. The relatively low physiological effort on the last three shod runs was unexpected and may be due to the slight rise in pace. Tentatively, it would appear that barefoot running is associated with lower physiological effort (perhaps 2%) when compared to lightweight running shoes (400g per pair), but another test with better controls is required!

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