Effect of Uphill Running on VO2, Heart Rate and Lactate Accumulation on Lower Body Positive Pressure Treadmills

dy positive pressure treadmills (LBPPTs) as a strategy to reduce musculoskeletal load are becoming more common as part of sports conditioning, although the requisite physiological parameters are unclear. To elucidate their role, ten well-trained runners (30.2 3.4 years; VO 2max: 60.3 4.2 mL kg 1 min 1 ) ran at 70% of their individual velocity at VO 2max(vVO 2max) on a LBPPT at 80% body weight support (80% BW Set) and 90% body weight support (90% BW Set), at 0%, 2% and 7% incline. Oxygen consumption (VO 2), heart rate (HR) and blood lactate accumulation (LA) were monitored. It was found that an increase in incline led to increased VO 2values of 6.8 0.8 mL kg 1 min 1 (0% vs. 7%,p< 0.001) and 5.4 0.8 mL kg 1 min 1 (2% vs. 7%,p<

support (90% BW Set), at 0%, 2% and 7% incline. Oxygen consumption (VO 2), heart rate (HR) and blood lactate accumulation (LA) were monitored. It was found that an increase in incline led to increased VO 2values of 6.8 0.8 mL kg 1 min 1 (0% vs. 7%,p< 0.001) and 5.4 0.8 mL kg 1 min 1 (2% vs. 7%,p< 0.001). Between 80% BW Setand 90% BW Set, there were VO 2differences of 3.3 0.2 mL kg 1 min 1 (p< 0.001) . HR increased with incline by 12 2 bpm (0% vs. 7%,p< 0.05) and 10 2 bpm (2% vs. 7%,p< 0.05). From 80% BW Setto 90% BW Set, HR increases of 6 1 bpm (p< 0.001) were observed. Additionally, LA values showed differences of 0.10 0.02 mmol l 1 between 80% BW Set and 90% BW Set. Those results suggest that on a LBPPT, a 2% incline (at 70% vVO 2max) is not yet suf cient to produce signi cant physiological changes in VO 2, HR and LA—as opposed to running on conventional treadmills, where signi cant changes are measured. However, a 7% incline increases VO 2and HR signi cantly. Bringing together physiological and biomechanical factors from previous studies into this practical context, it appears that a 7% incline (at 80% BW Set) may be used to keep VO 2and HR load unchanged as compared to unsupported running, while biomechanical stress is substantially reduced. Keywords:AlterG; anti-gravity treadmill; body weight support; graded running 1. Introduction To improve physical performance and to avoid overuse injuries, elite runners are increasingly using alternative training tools such as the lower body positive pressure tread- mill (LBPPT), an anti-gravity treadmill with an enclosed, air- lled chamber that generates positive pressure around the lower body [1]. Currently, it is known that running at the same velocity on LBPPT with partial body weight support is accompanied by a decrease in oxygen consumption (VO2) [1–8], heart rate (HR) [1,4,5,8] and blood lactate accumulation (LA) [2]—as compared to running under unsupported conditions. Furthermore, VO2max and HRmaxseem to be unaffected by LBPPTs [3,9]. The rst systematic review on this

[1]. Currently, it is known that running at the same velocity on LBPPT with partial body weight support is accompanied by a decrease in oxygen consumption (VO2) [1–8], heart rate (HR) [1,4,5,8] and blood lactate accumulation (LA) [2]—as compared to running under unsupported conditions. Furthermore, VO2max and HRmaxseem to be unaffected by LBPPTs [3,9]. The rst systematic review on this topic was given by Farina et al., 2017 [4]. The authors concluded that running on LBPPTs is effective in reducing impacts (i.e., peak Sports2021,9, 51.

Sports2021,9, 51 2 of 9 ground reaction forces). To still achieve the desired physiological stimuli (similar to those of an unsupported treadmill), faster running velocities and/or inclines need to be applied. Faster running velocities on the LBPPT are associated with an increase in physiological demand [1–3]. In turn, however, the increased velocity leads to higher ground reaction forces and loading rates [3,10–13]. Accordingly, velocity increases should be applied with caution. On the other hand, the factorinclinecould be suitable for increasing physiological demand while keeping biomechanical loads low. Recently, Farina et al. pointed out that there is a research gap on inclined running on a LBPPT, which “should be explored” [4] (p. 272). Especially because uphill running is an important training tool for middle and long distance runners [14]. Therefore, the purpose of the present study was to investigate the effects of LBPPT uphill running on VO2, HR and LA. Speci cally, the aim was to determine the in uence of three different inclines (0%, 2% and 7%) and of two different body weight support settings (80% BWSetand 90% BWSet) on the important physiological training parameters VO2, HR and LA [15–17]. In accordance with previous ndings on conventional treadmills (CON) and LBPPT, respectively, it was hypothesized, that (1) an increase in incline leads to higher VO2, HR and LA values, and (2) increasing body weight support is associated with a decrease in VO2, HR and LA. 2. Materials and Methods 2.1. Subjects Ten well-trained runners (30.2 3.4 years; VO2max= 60.4 4.2 mL kg 1 min 1 , Table) took part in the study. The participants were asked to avoid high-intensity and high-volume training sessions 48 h prior to the test and were informed in detail about the study design. Furthermore, the study was approved by the Ethics Committee of the Humboldt University Berlin and is in accordance with the Declaration of Helsinki. All participants provided written consent to participate in the study. Table 1. General characteristics of participants included in the study. VO 2: oxygen consumption; HR: heart rate. Measure Male ( n= 10) (min–max) Age (years) 30.2 3.4 (25.7–37.1) Body

study was approved by the Ethics Committee of the Humboldt University Berlin and is in accordance with the Declaration of Helsinki. All participants provided written consent to participate in the study. Table 1. General characteristics of participants included in the study. VO 2: oxygen consumption; HR: heart rate. Measure Male ( n= 10) (min–max) Age (years) 30.2 3.4 (25.7–37.1) Body mass (kg) 73.1 6.1 (63.7–82.2) Body height (cm) 178 6 (166–185) VO 2max(mL min 1 kg 1 ) 60.4 4.2 (54.9–68.4) vVO 2max(km h 1 ) 18.0 1.6 (16.0–20.0) HRmax(beats min 1 ) 193 8 (184–209) 2.2. Protocol and Test Design The participants completed four testing days in two weeks, at the same time of the day ( 30 min), with the same individual running shoes to avoid any footwear-related effects [18,19] and with a break between the tests of at least 48 h. The rst day, the partici- pants performed an incremental test on a regular treadmill h/p/cosmos saturn ® 250/100 (100% BWSet; h/p/cosmos sports and medical GmbH, Nußdorf-Traunstein, Germany) to determine VO2maxand velocity at VO2max(vVO2max). The initial running speed was set to 8 km h 1 and was increased by 2 km h 1 after each completed stage until volitional exhaustion. Stage duration was 3 min; between the stages there was a rest of 30 s. The second, third and fourth day, the participants started with a standardized warm-up of 10 min at 50% vVO2max. Subsequently, they ran a 6-min submaximal trial (twice 3 min, with a break of 30 s in between) at 70% vVO2maxon the LBPPT AlterG ® Anti-Gravity Treadmill ® Pro 200 Plus (AlterG ® , Fremont, CA, USA). Body weight was set to 80% BWSet and 90% BWSet, while incline was altered between 0%, 2% and 7%, in randomized order, resulting in 6 trials of 6 min for each subject. Before each testing day, body weight and height were measured (Seca Vogel and Halke Hamburg 910, seca GmbH and Co. KG,

2% and 7%, in randomized order, resulting in 6 trials of 6 min for each subject. Before each testing day, body weight and height were measured (Seca Vogel and Halke Hamburg 910, seca GmbH and Co. KG,

Sports2021,9, 51 3 of 9 Hamburg, Germany). Oxygen consumption was recorded using a stationary system with breath-by-breath analysis (Quark CPET, COSMED, Pavona di Albano, Italy). HR data were acquired using the HRM Run TM system (Garmin Ltd., Canton Schaffhausen, Switzerland). Before each trial, between the stages and directly after exhaustion of the VO2maxtest, a sample of 20 L of arterialized capillary blood was taken from the earlobe, solubilized in a 1000 L hemolysate solution and analysed using the SUPER GL ambulance system (Dr. Müller Gerätebau GmbH, Freital, Germany). Between the stages and after each test, rating of perceived exertion (RPE) was routinely analysed on the basis of the Borg RPE Scale (6–20) [20]. 2.3. Data Analysis VO2data processing was completed via the software OMNIA 1.6 (COSMED, Pavona di Albano, Italy). According to current research, VO2maxwas determined as the highest value averaged over 30 s [21]. As suggested, by Billat and Koralsztein [22], vVO2maxwas de ned as the lowest running velocity maintained for at least one minute that elicited VO2max. If a participant reached VO2maxbut did not maintain one minute of running, the velocity of the previous stage was used as vVO2max, as introduced by Kuipers et al. [23]. If, in turn, the running velocity was maintained for at least one minute (i.e., one third of stage duration), vVO2maxwas considered to be the running velocity of the previous stage plus one third of the increase between the two stages. Analogously, in case of two minutes maintained (i.e., two thirds of stage duration), vVO2maxwas approximated by be the running velocity of the previous stage plus two thirds of the increase between the two stages. Any other acquired submaximal VO2and HR data were averaged over 30 s, including the last 30-s-value of each stage for statistical analysis [21]. 2.4. Statistics To detect an effect of incline and BWSeton VO2, HR and LA data, two-way repeated measures analysis of variance (ANOVA) with Bonferroni posthoc tests were performed. To check sphericity, Mauchly's test was applied. If the assumption of sphericity was violated, the Greenhouse–Geisser correction was used. Data were processed with IBM SPSS Statistics 23

stage for statistical analysis [21]. 2.4. Statistics To detect an effect of incline and BWSeton VO2, HR and LA data, two-way repeated measures analysis of variance (ANOVA) with Bonferroni posthoc tests were performed. To check sphericity, Mauchly's test was applied. If the assumption of sphericity was violated, the Greenhouse–Geisser correction was used. Data were processed with IBM SPSS Statistics 23 (IBM, Armonk, NY, USA) and Microsoft Excel 2016 (Microsoft Corporation, Redmond, WA, USA). Results are presented as mean standard deviation. Standard level of signi cance was set top= 0.05, effect sizes were evaluated on the basis of eta squared (h 2 ). In addition, 95% con dence intervals (CI) were calculated. 3. Results 3.1. Oxygen Consumption (VO2) The effect of incline and BWSeton VO2is presented in Figure. Incline showed a sig- ni cant main effect (p< 0.001,h 2= 0.881), as did BWSet(p< 0.001,h 2= 0.954). A signi cant interaction effect between incline and BWSetwas not found (p= 0.429,h 2 = 0.076). Post hoc comparisons revealed a signi cant mean difference of 6.8 0.8 mL kg 1 min 1 between 0% incline and 7% incline (p< 0.001, CI: 4.3–9.3), and of 5.4 0.8 mL kg 1 min 1 between 2% and 7% incline (p< 0.001, CI: 3.2–7.6), respectively. No signi cant difference was observed for 0% vs. 2% incline (p= 0.117). Furthermore, between 80% BWSet and 90% BWSet, VO2differed by 3.3 0.2 mL kg 1 min 1 (p< 0.001, CI: 2.7–3.8).

Sports2021,9, 51 4 of 9Sports 2021, 9, x FOR PEER REVIEW 4 of 9 Figure 1. Oxygen consumption VO2 in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BWSet and 90% BWSet. Post hoc comparisons revealed a significant mean difference of 6.8 ± 0.8 mL kg −1 min −1 between 0% incline and 7% incline (p < 0.001, CI: 4.3–9.3), and of 5.4 ± 0.8 mL kg −1 min −1 between 2% and 7% incline (p < 0.001, CI: 3.2–7.6), respectively. No significant difference was observed for 0% vs. 2% incline (p = 0.117). Furthermore, between 80% BWSet and 90% BWSet, VO2 differed by 3.3 ± 0.2 mL kg −1 min −1 (p < 0.001, CI: 2.7–3.8). 3.2. Heart Rate (HR) The effect of incline and BWSet on HR is presented in Figure 2. A significant main effect was revealed for both incline (p < 0.001, η 2 = 0.657) and BWSet (p < 0.001, η 2 = 0.876). Furthermore, a significant interaction effect between incline and BWSet was not found (p = 0.766, η 2 = 0.029). Figure 2. Heart rate HR in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BWSet and 90% BWSet. Figure 1. Oxygen consumption VO 2in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BW Setand 90% BW Set. 3.2. Heart Rate (HR) The effect of incline and BWSeton HR is presented in Figure. A signi cant main effect was revealed for both incline (p< 0.001,h 2= 0.657) and BWSet(p< 0.001,h 2= 0.876). Furthermore, a signi cant interaction effect between incline and BWSetwas not found (p= 0.766,h 2 = 0.029).Sports 2021, 9, x FOR PEER REVIEW 4 of 9 Figure 1. Oxygen consumption VO2 in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BWSet and 90% BWSet. Post hoc comparisons revealed a significant mean difference of 6.8 ± 0.8 mL kg −1 min −1 between 0% incline and 7% incline (p <

2021, 9, x FOR PEER REVIEW 4 of 9 Figure 1. Oxygen consumption VO2 in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BWSet and 90% BWSet. Post hoc comparisons revealed a significant mean difference of 6.8 ± 0.8 mL kg −1 min −1 between 0% incline and 7% incline (p < 0.001, CI: 4.3–9.3), and of 5.4 ± 0.8 mL kg −1 min −1 between 2% and 7% incline (p < 0.001, CI: 3.2–7.6), respectively. No significant difference was observed for 0% vs. 2% incline (p = 0.117). Furthermore, between 80% BWSet and 90% BWSet, VO2 differed by 3.3 ± 0.2 mL kg −1 min −1 (p < 0.001, CI: 2.7–3.8). 3.2. Heart Rate (HR) The effect of incline and BWSet on HR is presented in Figure 2. A significant main effect was revealed for both incline (p < 0.001, η 2 = 0.657) and BWSet (p < 0.001, η 2 = 0.876). Furthermore, a significant interaction effect between incline and BWSet was not found (p = 0.766, η 2 = 0.029). Figure 2. Heart rate HR in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BWSet and 90% BWSet. Figure 2. Heart rate HR in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BW Setand 90% BW Set. Post hoc comparisons showed a signi cant mean difference of 12 2 bpm between 0% and 7% incline(p< 0.05,CI: 6–19), and of 10 2 bpm between 2% and 7% incline(p< 0.05, CI: 3–16), respectively. No signi cant difference was found for 0% vs. 2% incline(p= 0.793). Additionally, post hoc comparisons for 80% BWSetvs. 90% BWSetshowed mean differences of 6 1 bpm (p< 0.001, CI: 4–8). 3.3. Blood Lactate Concentration (LA) Figure Seton LA. Signi cant main effects could be observed for incline (p< 0.05,h 2= 0.397) and BWSet(p< 0.001,h 2= 0.783). A signi cant interaction effect between incline and BWSetwas not found (p= 0.069,h 2= 0.257). Despite

differences of 6 1 bpm (p< 0.001, CI: 4–8). 3.3. Blood Lactate Concentration (LA) Figure Seton LA. Signi cant main effects could be observed for incline (p< 0.05,h 2= 0.397) and BWSet(p< 0.001,h 2= 0.783). A signi cant interaction effect between incline and BWSetwas not found (p= 0.069,h 2= 0.257). Despite

Sports2021,9, 51 5 of 9 the clear main effect, the post hoc comparisons showed no difference between 0% and 2% incline (p= 1.000), 0% incline and 7% incline (p= 0.086) nor between 2% and 7% incline (p= 0.067). However, post hoc comparisons for 80% BWSetvs. 90% BWSetshowed mean differences of 0.10 0.02 mmol L 1 (p< 0.001, CI: 0.06–0.15).Sports 2021, 9, x FOR PEER REVIEW 5 of 9 Post hoc comparisons showed a significant mean difference of 12 ± 2 bpm between 0% and 7% incline (p < 0.05, CI: 6–19), and of 10 ± 2 bpm between 2% and 7% incline (p < 0.05, CI: 3–16), respectively. No significant difference was found for 0% vs. 2% incline (p = 0.793). Additionally, post hoc comparisons for 80% BWSet vs. 90% BWSet showed mean dif- ferences of 6 ± 1 bpm (p < 0.001, CI: 4–8). 3.3. Blood Lactate Concentration (LA) Figure 3 depicts the effect of incline and BWSet on LA. Significant main effects could be observed for incline (p < 0.05, η 2 = 0.397) and BWSet (p < 0.001, η 2 = 0.783). A significant interaction effect between incline and BWSet was not found (p = 0.069, η 2 = 0.257). Despite the clear main effect, the post hoc comparisons showed no difference between 0% and 2% incline (p = 1.000), 0% incline and 7% incline (p = 0.086) nor between 2% and 7% incline (p = 0.067). However, post hoc comparisons for 80% BWSet vs. 90% BWSet showed mean dif- ferences of 0.10 ± 0.02 mmol L −1 (p < 0.001, CI: 0.06–0.15). Figure 3. Blood lactate concentration LA in terms of 0% (green), 2% (yellow) and 7% (red) incline and compared for running on 80% BWSet and 90% BWSet. 4. Discussion The present study is, to the best of our knowledge, the first to examine how uphill running on a LBPPT effects VO2, HR and LA. Confirming our initial hypothesis, it could be observed that an increase in incline on LBPPT generally leads to higher VO2 and HR. However, no significant difference could be determined for

This study investigates the effects of uphill running on physiological parameters using LBPPTs.