5.1 Responses during exercise
During steady-state running, V̇O2 and RPE were higher (by 4.5% and 7.7%, respectively) and HR was 0.4% lower during experimental trials wearing the resistance garment than during control trials wearing a standard pair of exercise shorts, although the magnitudes of difference were trivial to small, and not statistically significant. There was large inter-individual variability; V̇O2 was higher in experimental trials for 10 of the 15 subjects (range: 0.4-12.0% higher compared to control trials) and HR was lower in experimental trials for nine of the 15 subjects (range: 0.3-5.5% lower compared to control trials). The V̇O2 response to exercise in this study is consistent with previously reported findings that lower limb loading increases the metabolic cost of exercise when compared to exercising in unloaded conditions (9-11). Whilst the increase in V̇O2 during the experimental trials was of small effect in the current study (r = 0.24), the magnitude of this increase (4.5%) is greater than that reported by Martin (9) who attached 0.5 kg weights to the thighs and feet (1.7% and 3.3% respectively) and attached 1.0 kg weights to the thighs (3.5%) during continuous running. Others have reported similar increases in V̇O2 to the present study during submaximal running; Claremont and Hall (10) reported a 4.5% increase with the use of 0.45 kg ankle weights and Field et al. (11) reported an increase of 4.3% with the use of weighted pouches stitched into compression shorts equating to 3% BM resistance. Comparable increases in V̇O2 between the current study and previous research indicates the method of application of load to the garment in the current study (i.e. resistive bands woven into the material of the resistance garment) has similar potential to increase the metabolic demand as previously reported methods, with the added benefit of improved design features. However, caution should be used when generalising these findings as five of the 15 subjects in the current study recorded a lower V̇O2 in experimental trials (range: 1.9-3.8% lower compared to control trials), suggesting that the current WR garment may not influence the metabolic demand of running for everyone equally. Likely explanations for this may relate to differences in body morphology or the approach used to prescribe exercise intensity in the current study (i.e. assigning running speed based on physical activity levels vs. using a relative percentage of each subject’s V̇O2max). Nevertheless, there is a trend to suggest that the magnitude of applied resistance provided by the garment in the current study (1-3% BM) is likely sufficient to provide a stimulus that increases V̇O2 during a single bout of exercise. This finding supports those of Field et al. (11) who also observed 1.7%, 2.4% and 4.3% increases in V̇O2 when 1%, 2% and 3% BM resistance, respectively, were applied via lower limb loading during running. However, Field et al. (11) also observed 5.4% and 8.1% increases in V̇O2 when 4% and 5% BM resistance was applied, respectively, suggesting that V̇O2 may indeed continue to increase with increasing WR load. Therefore, future research is warranted to investigate an “upper limit” of WR that results in an increase in V̇O2 without a concomitant decrease in movement quality. Future research should also extend on the present investigation and assess whether the current WR garment elicits a similar V̇O2 response during exercise exceeding 10 minutes in duration and/or exceeding submaximal intensities that are individualized to each subject’s V̇O2max.
The perceived impact of the WR garment was insignificant, as shown by only a slightly higher RPE during the experimental (14 [3.0]) compared to the control trial (13 [3.0]). Two previous studies have examined the perceived impact of WR and external loading on the user during running and walking; both studies reported considerable increases in RPE when the % of BM resistance was increased using weighted back packs (8) and compression shorts (11). Key methodological differences may explain, at least in part, why the present results do not align with those previously reported. The current study only assessed 1-3% BM resistance whereas Simpson et al. (8) assessed 20%, 30% and 40% BM resistance. In the current study, subjects completed 2 x 10-minute steady-state runs with five days between trials whereas in the study by Field et al. (11), subjects completed 6 x 8-minute submaximal runs over two separate testing sessions with only 2-3 days recovery between sessions. Additionally, it is unclear whether higher RPE scores in the Simpson et al. (8) study were the result of increases in BM resistance or a reflection of discomfort experienced by the subjects given the high discomfort ratings reported in the shoulders, neck, upper back, lower back, hips, thighs and lower legs. Although results from the current study do not support those from previous literature, the differences across studies highlights the need to further examine the perceived impact of WR during exercise using a variety of WR methods and applied magnitudes of resistance. Additionally, future research should also consider other perceptual measures that the current study did not explore such as comfort, to determine the practicality of WR methods more holistically.
In contrast to V̇O2, there was no difference in HR responses to exercise between the experimental and control trials. Indeed, HR was actually 0.4% lower in the experimental compared to control trials, although the effect size was trivial (r = -0.05). This finding is unique when compared to previous literature as a variety of studies using lower limb loading (9-11) and upper body loading (8) noted an increase in HR when incorporating WR during exercise. Claremont and Hall (10) observed a 2.7% increase in HR when 0.45 kg ankle weights were used during continuous running. Martin (9) noted HR increases of 0.5% and 1.6% when 0.50 kg lead shot weights were attached to the thigh and feet respectively, and 1.4% and 3.4% HR increases with 1.0 kg lead shot weights attached to the aforementioned body segments. Field et al. (11) also reported increases in HR (0.4%, 1.5% and 1.8%) when 1%, 2% and 3% BM resistance was applied, respectively, via weighted pouches stitched onto compression shorts during sub-maximal running. Differences in the methods of WR used, and the loads applied between the current study and others may explain, at least in part, why different HR responses were seen. The general design of the garment in the present study and use of resistive bands may not provide consistent and/or sufficient load or resistance to influence HR during locomotion when compared to the addition of weighted pouches or lead shots used in previous research (9, 11). However, further studies incorporating biomechanical analyses are needed before making conclusions regarding loading over a gait cycle. Additionally, the garments were not designed to specifically fit each subject’s individual body shape and size which may explain, at least in part, why nine of the fifteen subjects in the present study recorded a lower HR overall during experimental than control trials (range: 0.3-5.5% lower). The magnitude of HR increases in previous literature is lower than the magnitude of increase seen for V̇O2 (9-11), and this is consistent with the present study. This may suggest that V̇O2 is more sensitive to identifying a change in physiological load with WR, and therefore HR may have a higher threshold for detecting additional load applied in the form of WR garments. Future research examining the different detection limits of V̇O2 and HR over a range of resistances is needed to confirm this observation and identify their respective sensitivity thresholds.
5.2 Responses during passive recovery
During passive recovery following steady-state running, V̇O2 and HR were lower (by 4.7% and 4.3%, respectively) during the experimental than the control trial and the magnitudes of difference were small and not statistically significant. V̇O2 was higher in experimental comparted to control trials for ten of the fifteen subjects (range: 4.4-33.4% higher) and HR was lower in experimental compared to control trials for nine of the fifteen subjects (range: 2.2-12.6% lower), indicating large inter-individual variability in responses. This variation in individual responses highlights the need for caution when generalising the main findings of the present study, especially given the small sample size. Nevertheless, this finding might hold some practical significance, since even small improvements in recovery might be valuable for exercise involving repeated efforts, such as high-intensity interval training where the intensity of the subsequent exercise bout is influenced by the preceding recovery bout (26, 27). This finding is unique given the current study is the first to analyse the impact of lower limb WR on acute recovery following exercise as well as assessing a unique application of WR wholly contained within a garment and not using external weights. These findings provide a foundation for future research to investigate the influence of exercise intensity, duration and nature (continuous vs. intermittent) on recovery whilst wearing WR garments. The design of the garment used in the present study may explain, at least in part, why a small improvement in physiological recovery was seen during the experimental trial. The overall design and materials used ensured the garment smoothly conformed to the user’s individualized body shape creating a tight fit, similarly to a compression garment. Recent research has shown whole-body compression garments significantly reduced HR following incremental running tests in untrained subjects when compared to non-compression garments (28, 29). When applied to garments, compression is proposed to improve recovery by mitigating the physiological strain of exercise via increased localized blood flow and provision of oxygen and improved venous return to remove metabolites following exercise (14). While these mechanisms may partly explain the small reductions in V̇O2 and HR during passive recovery post-exercise, results should be interpreted with caution when determining the capacity of the garment to promote post-exercise recovery. These findings support the need for future research to further explore the impact of WR on recovery and the physiological mechanisms responsible. The measurement of additional metabolic variables such as blood lactate concentration may also be beneficial when exploring the extent to which WR increases the physiological demand of exercise, and its impact on post-exercise recovery.