Running economy (RE) is a critical element of running performance for elite runners. Research has shown that RE is a better predictor of running performance than maximal oxygen uptake (V[Combining Dot Above]O2max) (15) with as much as 65.4% of race performance explained by variations of RE among elites with similar V[Combining Dot Above]O2max values (1). For the purpose of this study, RE will be defined as the energy requirement for a given speed during submaximal running measured by consumption of oxygen (V[Combining Dot Above]O2) while at steady-state.
Although it has been surmised that RE is partly inherent (2), several studies have suggested that RE may be improved by a variety of modalities including strength, plyometric, and altitude training without corresponding improvements in V[Combining Dot Above]O2max (8,12,13,16,17,19,22). Relatively small improvements in RE may result in substantial reductions in finishing time depending on the event, possibly altering the outcome in competition.
In the past decade, backwards walking (BW) and backwards running (BR) have gained popularity, primarily in the rehabilitation setting, as a form of low-impact exercise. Research suggests BW and BR may provide benefit for a variety of conditions including lower back pain, knee osteoarthritis, hamstring inflexibility, and side-effects of stroke (3,7,18,23,24). The outcomes of these studies have included reduced pain, increased flexibility, walking speed, and walking symmetry indexes.
Additionally, studies have been conducted to measure the metabolic cost of backwards locomotion and raised the question of a potential training application in healthy individuals (5,10,21). One such study conducted by Flynn et al. (5) found that BW and BR resulted in greater submaximal V[Combining Dot Above]O2 response, heart rate, and blood lactate than at the same speeds in the forward direction. The researchers concluded that an injured athlete may be able to maintain cardiovascular fitness by utilizing BW and BR during rehabilitation.
The primary purpose of this study was to measure the effects of sustained BR training on forward RE. It was hypothesized that BR training would improve forward RE in trained male runners.
Experimental Approach to the Problem
The protocol was reviewed and approved by the institutional review board (IRB) at the University of Dayton. The design was a 10-week BR training study, with training sessions held twice a week with at least 48 hours between each session. There were a total of 20 training sessions per subject and each session was monitored by the primary investigator. All testing and training sessions were conducted on a calibrated laboratory treadmill (True Fitness Technology, St. Louis, MO, USA) located at the University of Dayton.
Eight healthy, trained male runners (26.13 ± 6.11 years, 174.7 ± 6.4 cm, 68.4 ± 9.24 kg, 8.61 ± 3.21% body fat, 71.40 ± 7.31 ml·kg−1·min−1) were selected to participate in this study following completion of an informed consent document approved by the University of Dayton IRB. Inclusion criteria were males between the ages of 18 and 40, training volume of at least 150 minutes per week, V[Combining Dot Above]O2max equal to or greater than the 80th percentile in their respective age groups (14), no significant injuries within the last year, and consistent training over the last 6 months. Subjects were asked to replace forward running (FR) time in their training outside of the study in a 1:1 ratio with the BR they performed while enrolled in this study. Subjects were training for events ranging from the 5K to the marathon and ran 5–7 days a week on their own outside of the study.
In accordance with the timeline of study (Figure 1), subjects were tested at baseline (week 0), familiarized (week 5), and post-training (week 11) with both a ramped V[Combining Dot Above]O2max protocol designed for a trained male population (1) and an economy test protocol using speeds from previous studies (11,22). The latter consisted of a 4-minute warm-up at 188 m·min−1 followed by 10 minutes of steady running at 215 m·min−1. Both the maximal test and the economy test were measured with a TrueOne 2400 metabolic cart (Sandy, UT, USA) and HansRudolf 3813 Pneumotachometer (Shawnee, KS, USA). The V[Combining Dot Above]O2max and economy tests were separated by at least 48 hours and performed in that order, respectively. Body composition was measured with a Bod Pod (COSMED, Italy) immediately preceding the economy test during each testing phase.
Following baseline testing, subjects were given a 5-week familiarization period using a harness, treadmill, and running backwards. This was performed to allow participants to accommodate to any of the biomechanical differences of performing the new movement of BR. Subjects trained with harness (Biodex Unweighing System; Shirley, NY, USA) as a safety precaution; however, no body weight support was provided. Each training session began with 4 minutes of BR at 107 m·min−1 as a warm-up. Subjects were given the option to walk or run at this speed as per the findings of Terblanche et al. (20). The speed was then increased to 134 m·min−1 for the first 5-week run-in period, and to 161 m·min−1 for the second 5 weeks of the actual study. Weeks 1 and 6 started with 15 minutes of BR and increased by 1 minute each week until 19 minutes of steady BR was accomplished on weeks 5 and 10. Ratings of perceived exertion (RPE) were collected at 5-minute intervals throughout the training on a 0–10 scale while heart rate (HR) was collected every minute.
Upon completion of data collection, paired t-tests were conducted on all the measured variables from baseline to familiarized, and familiarized to post-training using SPSS Statistics 22 software (IBM, Armonk, NY, USA). Statistical significance was selected at α = 0.05.
Compliance of this study was 100% for all 8 subjects. Anthropometric and economy data can be found in Table 1. There were no statistically significant differences between any of the baseline and familiarized variables.
After 5 weeks of BR training from familiarized to post-testing, body mass, lean mass, fat mass, and % body fat remained unchanged (p > 0.05).
Forward running steady-state economy V[Combining Dot Above]O2, HR, and RPE scores were determined by averaging the last 3 minutes of the economy tests. Mean running economy V[Combining Dot Above]O2 response improved by 2.54% (1.19 ± 1.26 ml·kg−1·min−1, p = 0.032) at 215 m·min−1 with 7 of the subjects improving their running economy. However, neither running economy HR nor RPE changed (p = 0.908 and 0.197, respectively) after the BR training. Figure 2 depicts each subject's economy test V[Combining Dot Above]O2 scores whereas Figure 3 displays each subject's recorded economy HR data.
The training heart rates for BR were unchanged throughout the training period from familiarized to post-testing.
This study attempts to evaluate the effectiveness of BR as a mode of training to improve RE at submaximal speeds. Previous research suggests that backwards locomotion uses the same motor pattern as forward locomotion but in the reverse direction (4) and requires greater metabolic demand, energy expenditure, and cardiorespiratory response than that of forward movement (5,6,10). These findings suggest the potential for a training effect if used regularly.
The subject population of this study, while specialized, was important to evaluate. To the knowledge of the investigators, subjects of this fitness level and experience had yet to be trained with BR to improve RE. However, Terblanche et al. (21) tested 26 habitually-active young females with half of them in a BW and BR training group and the remainder in a matched control group. The researchers found the BR trained group improved from baseline in skinfolds, body fat %, and predicted V[Combining Dot Above]O2max after 6 weeks of training, 3 times a week. The study began with 15 minutes of BR and finished with up to an hour of time being devoted to 60% of BR and 40% of BW. Interestingly, the training group's forward and backward RE improved by 32% and 30%, respectively, at submaximal speeds. The control group remained unchanged in all test variables. The researchers concluded that BR and BW training can improve cardiorespiratory fitness and body composition in young women.
This study evaluated a much different demographic of athletes with less room for improvement in most aspects of fitness and body composition. As a result, V[Combining Dot Above]O2max and body composition were not expected to change throughout the study. This may have failed to occur due to the short time frame of the study and the high level of fitness of the subjects.
The change economy V[Combining Dot Above]O2 (relative to body mass) likely occurred as a result of the BR training and not simply as a result of a change in weight. Despite the subjects gaining 1.04% of their total body mass, a nonsignificant finding, after the training, they noticed a decrease in oxygen consumption at the same test speed, 215 m·min−1. Additionally, the subjects continued training outside of the experiment but replaced FR with BR in a 1:1 ratio to avoid an additive effect of increased time of training.
Similar results have been reported after strength, plyometric, and altitude training interventions. Testing individuals with V[Combining Dot Above]O2max values with mean scores of 71.0, 69.7, and 71.7 ml·kg−1·min−1, researchers of each study found improvements of 3.20, 4.74, and 4.10%, respectively, in running economy (12,16,17). The magnitude of change was greater in these studies than the current research while using individuals of similar aerobic capacities, however, the interventions were much longer in duration, training their subjects for 7, 14, and 9 weeks compared with 5 weeks used in this study.
Based on the results of the current study, BR may be a viable method of training for healthy, trained male runners to reduce the oxygen cost of submaximal running. These data are particularly encouraging based on the relatively short intervention period of 5 weeks, meeting only twice a week, compared with other studies ranging from 6 to 14 weeks and meeting at least twice a week during that time (1,2,9,12,15,21,22).
Future studies could be conducted with subjects of different training statuses and demographics, because this was a limitation in this study. These studies may use a control group to compare against the intervention group while using a larger number of subjects. The mechanism for improvement in RE could be further studied. With no change in heart rate during the economy test, it is speculated that a change occurred in the peripheral delivery of oxygen to the skeletal muscle as opposed to cardiac output. However, more research should be conducted to compare individualized responses with BR training and heart rate response, as 3 subjects reported a distinct decrease in heart rate after training whereas 3 subjects reported a distinct increase in heart rate after training. Furthermore, the skeletal muscle may also have become more efficient in using the delivered oxygen. More research is required to address these questions.
Five weeks of BR training improved forward running economy by 2.54% in healthy, trained male runners without improving V[Combining Dot Above]O2max or altering body composition. The improvements observed in this study could possibly be a beneficial form of training to an already highly trained population to improve running economy.
The data of this study suggest that running backwards several times a week may be a form of training that healthy, highly trained male runners could use to improve their RE in the forward direction. The improvement in RE may translate to improved performance in their respective race distances, as most of the variation in race finish time is a factor of RE among individuals with similar cardiorespiratory fitness. Strength and conditioning coaches as well as distance running coaches may find BR training beneficial to the performance of their athletes. Exercise specificity may make BR a more practical economy-improving activity than other methods currently in use.
We thank all the runners who participated in this study for their time, effort, feedback, and compliance.
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