Objective: To investigate which footwear provides for greater cardiovascular fitness improvement with fewer injuries: Kangoo Jumps—boots with a cantilever spring system designed to dissipate impact forces—or conventional running shoes.
Method: Thirteen subjects (designated NG) completed a 12-week, three-session-per-week training program using normal running shoes, and a comparable group of 12 subjects (designated KG) did the same using Kangoo Jumps. Peak oxygen uptake (VO2 peak) and ventilatory threshold (Vt) were measured before and after the training program using a continuous treadmill protocol. All data underwent analysis of covariance (ANCOVA) using age as a covariate; injury rates were analyzed with a chi-square 2x2 contingency table; the alpha level was set at .05 for all statistical calculations.
Results: VO2 peak significantly increased in the KG subjects compared with NG subjects, (P <.05). Vt was not significantly different between groups. NG subjects had a significantly greater incidence of lower leg injuries when compared with KG subjects (χ21 = 6.7, P <.05). A criterion of 1 week of missed training was required for all of the 42.9% lower leg injuries.
Conclusion: From these data, it appears that Kangoo Jumps provide an effective means of aerobic training and a reduced risk of injury when compared with conventional running shoes.
Running is one of the oldest and simplest types of aerobic activity. Unfortunately, running also has very high injury rates. For example, Macera and colleagues reported that 24% to 65% of runners can expect to experience a running-related injury in a typical training year. Running imposes a ground reaction force of 2 to 2.5 times body weight with each step, meaning the likelihood of injury through overuse in the lower limb and pelvis is very high. Kangoo Jumps (Figure 1) are an example of new technology using a cantilever spring system designed to reduce running-related injury by dissipating up to 60% of the impact forces experienced through the ankles, knees, hips, and back.
The study described here was designed to assess the effectiveness of Kangoo Jumps as a training device by comparing subjects using Kangoo Jumps with subjects using conventional running shoes. It was hypothesized that after a 12-week training program the subjects using Kangoo Jumps would show greater improvement in cardiovascular fitness than subjects wearing normal running shoes. It was also hypothesized that subjects using normal running shoes would have a greater incidence of injury than those using Kangoo Jumps.
Twenty-five novice runners volunteered to participate in a 12-week aerobic exercise program based on the standardized InTraining clinics organized by the Sport Medicine Council of British Columbia. All subjects were training for the 10-km Vancouver Sun Run. None had participated in a regimented aerobic program in the 6 months prior to the study.
The subjects were divided into two groups: a Kangoo Jumps group (designated KG; n = 12; age 25.4 ± 5.3 years; weight 67.4 ± 18.0 kg) and a group using normal running shoes (designated NG; n = 13; age 28.8 ± 4.7 years; weight 75.1 ± 25.2 kg). Both groups completed the same training program and were led by a certified leader.
All subjects committed to three training sessions per week for 12 weeks; they followed an InTraining clinic leader for one session and completed the other sessions independently. The training program consisted of walk/run repetitions, increasing in total duration from 20 to 65 minutes per session. The first session began with a short jog (30 seconds) and a 4.5-minute walk, repeated 7 times. The participants’ running time and distance gradually increased each week for the entire 12-week program. (For details about the InTraining walk/run program, see the SportMedBC web site at www.sportmedbc.ca.) All subjects kept a training log for the duration of the 12-week program, monitoring their adherence to the program and the intensity of their workouts. The training logs were used to record heart rate and rating of perceived exertion (RPE). (It should be noted that the training log data received from subjects was limited by their ability to assess these measures during their independent sessions.)
During the training period, subjects were classified as injured if they met at least one of the following criteria.[5,6]
• Experienced pain or symptoms during or immediately after a run.
• Experienced pain or symptoms within approximate time span of start of running program.
• Felt that an injury was related to running.
• Stopped running or significantly reduced running mileage and sought medical attention because of injury.
• Stopped running for at least 1 week because of injury.
Aerobic capacity can be assessed in a variety of ways. Traditionally, the peak amount of oxygen uptake (VO2 peak) is the most commonly used measure of aerobic capacity. The American College of Sports Medicine has stated that a minimum of 50% of VO2 peak must be maintained in order to gain cardiovascular benefits. In addition, we know that the range of VO2 improvements after an aerobic training program will vary enormously, depending on factors such as initial fitness level, training intensity, and frequency and duration of activity. Despite this variability, typical changes in VO2 peak range from 5% to 10%.
More recently, other measures that explore concepts such as efficiency are becoming increasingly popular. One such measure is that of ventilatory threshold (Vt). Ventilatory threshold is thought to be a measure of the body’s inability to maintain exercise using aerobic metabolism, which leads to an increased use of the anaerobic system and consequent development of metabolic acidosis. The ventilatory threshold, therefore, is a nonlinear increase in the expired gas volume as the level of exercise intensity increases. The Vt can be described as the VO2 at which the ventilatory deflection occurs, or as the percent (%)VO2 peak at which the deflection occurs. Physical fitness is known to be one of the main factors that influence the values of percent VO2 peak at Vt.
All participants had their VO2 peak measured during week 1 and at the end of week 12. The continuous treadmill protocol started at 4 mph then increased 0.5 mph every minute up to 8 mph, at which point the grade increased 2% per minute. The subjects stopped the test when they felt they had reached their volitional fatigue point. All expired gases were collected and analyzed using the Vmax metabolic cart (V6200, SensorMedics Corp, Yorba Linda, CA). Heart rates were measured using Polar Vantage HR monitor (Polar Electro, Finland).
The data from the treadmill tests were analyzed using the SPSS software package. Analysis of covariance (ANCOVA) was used to determine if there was a significant change in VO2 peak over the span of the training program, with age as a covariate. A two-way mixed ANCOVA was used to analyze the ventilatory threshold data. Chi-square 2x2 contingency tables were used to determine frequency of injuries between the two groups. These data are reported as mean ± standard error analyzed with significance set at P <.05, unless otherwise indicated.
On average, the age of subjects was not significantly different between the two groups (ts23 = 1.71 years, P >.05). However, to ensure age had no effect on the results, it was used as a covariate with ANCOVA. The mean weight change over the span of the training program was also not significant (NG: –1.08 ± 0.585 kg; KG: –0.79 ± 0.594 kg; P >.05).
VO2 peak improvement
The mean pre-intervention VO2 peak was not significantly different between groups (NG 41.06 ± 1.22 mL/kg/min-1; KG 43.22 ± 2.14 mL/kg/min-1). However, in the KG subjects, mean VO2 peak increased significantly by 18.3% (+7.8 ± 0.97 mL/kg/min-1) compared with the NG subjects’ increase of only 3.7% (+1.3 ± 0.93 mL/kg/min-1) after completion of the training program (t22.3 = 4.80, P = .001). Figure 2 describes the change in VO2 peak for the two groups.
Ventilatory threshold (Vt)
The thresholds were calculated using the excess CO2 (ExCO2) elimination curve and determined by two external reviewers to identify the percent VO2 peak where CO2 demonstrated a sudden and sustained increase (Vt). Age correlated with pre-intervention Vt (r = 0.40, P = .046), and was entered as a covariate into a two-way mixed ANCOVA. Both groups saw an increase in VO2 at Vt, with the KG subjects demonstrating a greater increase than NG subjects (7 .9% ± 10.47 compared with 2.59% ± 6.41, respectively, t17.97 = 1.51, P = .15). ANCOVA data revealed no significant difference between the degree of change of VO2 at Vt. Figure 3 shows the VO2 (mL/kg/min-1) at which Vt was reached.
NG subjects were found to have a significantly greater incidence of injuries when compared with KG subjects (?21 = 6.7, P <.05). Injuries reported by subjects included:
• Iliotibial band friction syndrome
• Anterior tibial pain
• Ankle sprain
• Plantar fasciitis
Six of 13 NG subjects (42.8%) experienced injuries. Three were unable to complete their goal of running the Vancouver Sun Run, and one subject was not able to complete the posttraining treadmill test. None of the 12 KG subjects (0%) experienced injuries, although some did experience minor problems associated with wearing Kangoo Jumps. These problems (arch pain and blisters) required a reduction in training for no more than two sessions.
Although the data show that KG subjects had a statistically significant improvement in VO2 peak compared with NG subjects, no research has been done to measure the effectiveness of the InTraining running program to improve aerobic capacity; therefore, the mean VO2 peak data from this study could not be compared with other data.
A number of factor may explain the extent of VO2 peak improvement found in this study (3.7% for NG subjects and 18.3% for KG subjects): initial fitness; duration of training program; intensity, duration, and frequency of individual training sessions. Since we know baseline fitness levels for the two groups of subjects were not significantly different, we may assume that NG subjects either did not complete their training sessions at an intensity level near 50% of their VO2 peak or did not follow the program directions. All subjects had been properly educated to record RPE and heart rate in compliance with the program directions, but NG subjects may have lacked the ability to monitor their own exertion levels during their sessions.
The difference in posttraining VO2 peak may also be a result of the Kangoo Jumps mechanism. This mechanism requires the subject to compress the tension band in order to propel the body forward. Because walking and running in this way requires more effort, the subject using Kangoo Jumps expends more energy per walk/run session, requires more oxygen, and makes greater demands on the cardiovascular system than the subject using conventional runners.
Although both groups did show an increase in VO2 at Vt post-intervention, with KG subjects demonstrating a greater increase than NG subjects, a two-way mixed ANCOVA showed that these results were not significant (P >.05). The lack of a significant change in VO2 at Vt between and within groups may be partly due to the relatively large standard deviation resulting from the small sample size and the few subjects with very large changes in VO2 at Vt. The lack of significant change may also be partly due to the intensity of the training, which may not have been sufficiently high to result in an increase in VO2 at Vt. The intensity of the exercise must be high enough to recruit the anaerobic metabolism and so needs to be near the ventilatory threshold in sedentary subjects and slightly above in trained subjects. Therefore, the amount of change may have been dependent on initial fitness level. Future research into VO2 at Vt must take these study limitations into account.
Although KG subjects did not experience any defined injuries, they did experience some minor problems.
Arch pain was an initial problem experienced by 58% of KG subjects. This pain subsided once the subjects became accustomed to the fit of the boots during a 2-week adjustment period.
Major blisters in the arch of the foot were experienced by 30% of the KG subjects. The most effective treatment for this included resting for two sessions, then using wicking socks to remove moisture from the foot, thus reducing the abrasion that caused the blisters, and using lubricating cream to reduce the friction between the foot and the bootliner.
Bruising and swelling around the lateral and medial malleoli was experienced by 25% of KG subjects. This was remedied with either a gel sock that provided more padding for subjects with bony ankles, or with a large foam ring taped into place around the malleolus. (Jumps International Inc. is currently developing another softer boot that they hope will reduce bruising and swelling.)
The study showed that while Kangoo Jumps are suitable for most body types, some people with larger calves may not be able to get a snug fit around the foot and ankle. If the boot does not fit properly the subject will not have enough support to sustain long periods of walking or running.
Results from this preliminary assessment of Kangoo Jumps suggest that using Kangoo Jumps rather than normal running shoes can have a greater effect on cardiovascular fitness improvement. Results also suggest that Kangoo Jumps might be an effective tool for the rehabilitation of lower leg injuries. More research is needed to explore the use of Kangoo Jumps for rehabilitation. Research is also needed to measure possible aerobic capacity improvement and determine a mean increase in VO2 peak after training. All of these research aims would be furthered with larger sample size, matching subjects, and a true random assignment research design.
This study was supported by Jump Canada Sales Inc.