Repeated Bout Effect of Downhill Running on Physiological Markers of Effort and Post Exercise Perception of Soreness in Trained Female Distance Runners

his study examined the effect of repeated bouts of level and downhill running on physio- logical markers of effort and exercise-induced muscle soreness in trained female distance runners. Ten participants (Age: 24.4±2.0 years;˙VO 2peak: 52.9±1.1 mL·kg −1 · min −1 ), naïve to downhill running, completed six alternate 5 min trials of level and downhill running (−15%) at a 70% velocity at˙VO 2peakon two occasions, three weeks apart. Perceived muscle soreness was measured upon completion and in the 72 h post exercise.˙VO 2, Heart Rate (HR), Blood Lactate (BLa), and Respiratory Exchange Ratio (RER) were lower running downhill (p< 0.016,ηp 2 > 0.541). For the first downhill run, Rating of Perceived Exertion (RPE) was higher compared to that for level running (p= 0.051; d =0.447), but for the remaining trials, RPE was lower when running downhill (p< 0.004;d >0.745). ˙V O 2, HR, and RER were not different in the second bout (p> 0.070,ηp 2 < 0.318); however,˙VO 2 was lower in each downhill trial (∆= 1.6–2.2 mL·kg −1 · min −1 ;d= 0.382–0.426). In the second bout, BLa was lower (p= 0.005,ηp 2 = 0.602), RPE in the first

RPE was lower when running downhill (p< 0.004;d >0.745). ˙V O 2, HR, and RER were not different in the second bout (p> 0.070,ηp 2 < 0.318); however,˙VO 2 was lower in each downhill trial (∆= 1.6–2.2 mL·kg −1 · min −1 ;d= 0.382–0.426). In the second bout, BLa was lower (p= 0.005,ηp 2 = 0.602), RPE in the first trial was lower (p= 0.002;d =0.923), and post exercise perceived soreness of the gastrocnemius, quadriceps, and hamstrings was attenuated (p< 0.002;ηp 2 > 0.693). Perceived soreness of the gluteal muscles was lower in the second bout immediately post exercise, 24 h, and 48 h post exercise (p< 0.025;d >0.922). A repeated bout of downhill running attenuated perceived muscle soreness and may modulate the physiological and perceived physical demand of a second bout of level and downhill running. Keywords:exercise physiology; eccentric exercise; delayed onset of muscle soreness; endurance; running 1. Introduction Downhill running has been used as a model to explore the physiological consequences of eccentric muscle activity and the effects of exercise-induced muscle damage [1]. Running at a negative gradient increases the negative velocity of the centre of mass, resulting in altered gait kinematics and increased eccentric action of the lower limb musculature, which aids in controlling deceleration and managing impact transients during the first period of foot ground contact. Given that eccentric force generation physiologically differs from other forms of muscle ctivity [2] and that an unaccustomed increase in eccentric muscle action evokes tissue damage [3], downhill running and its consequences are physiologically and biomechanically distinct. The acute effects of downhill running on gait biomechanics and running energetics have been thoroughly explored. It is established that downhill running at an equivalent velocity to level running results in reduced˙VO2, Respiratory Exchange Ratio (RER), Heart Rate (HR), and metabolic power [4–6], and, as such, is less metabolically demanding. Such effects are primarily attributed to an increase in metabolically efficient eccentric muscle actions [7]. Biomechanically, downhill running results in an increased stride frequency, Sports2024,12, 169.

Exchange Ratio (RER), Heart Rate (HR), and metabolic power [4–6], and, as such, is less metabolically demanding. Such effects are primarily attributed to an increase in metabolically efficient eccentric muscle actions [7]. Biomechanically, downhill running results in an increased stride frequency, Sports2024,12, 169.

Sports2024,12, 169 2 of 12 increased aerial time, and decreased duty factor when compared to level running [8], where such effects may contribute to an improved running economy, but also help in reducing the elevated impact transients evoked by downhill running. The reduced metabolic cost of downhill running is not incremental given the increased metabolic demand of energy dissipation [4]. Evidence indicates that, at gradients of−20% and greater, the energetic cost of running begins to increase [8]. Furthermore, due to an increase in unaccustomed eccentric muscle actions, downhill running evokes exercise-induced muscle damage, and the post exercise effects and time course of recovery has been thoroughly explored. Specifically, an initial novel bout of downhill running evokes reduced skeletal muscle contractile function, reduced running economy, an increased perception of pain, and the elevation of several biochemical markers of muscle damage and inflammation [9–14], which all persist for days following the downhill running bout. Unaccustomed eccentric exercise has also been shown to elicit a repeated bout effect (RBE), where skeletal muscle adapts to exercise-induced damage via several protective mechanisms to promote resistance to subsequent muscle-damaging activity [15]. Whilst the time course of effects is not well explored, evidence suggests that protection induced from the initial bout of damaging exercise can persist for up to six months [16]. Although work is ongoing to more precisely elucidate the underlying mechanisms, evidence suggests that the RBE can manifest due to a shift toward the preferential recruitment of low-threshold motor units and improved motor unit synchronisation, altered tendon compliance, remodelling of the skeletal muscle extracellular matrix, and modified inflammatory responses [15], which, mechanistically, may lead to changes in the physiological demand of the activity. Several studies have examined the RBE of downhill running, typically focusing on the impact of the first bout on exercise-induced muscle damage following the subsequent bout. There is consensus in the literature that a repeated bout of the same downhill running protocol attenuates the post-exercise increase in circulating creatine kinase activity, immunoglobulin concentration, and markers of oxidative stress and reduces the magnitude and recovery of losses in maximal voluntary contractile function and

the impact of the first bout on exercise-induced muscle damage following the subsequent bout. There is consensus in the literature that a repeated bout of the same downhill running protocol attenuates the post-exercise increase in circulating creatine kinase activity, immunoglobulin concentration, and markers of oxidative stress and reduces the magnitude and recovery of losses in maximal voluntary contractile function and the perception of muscle soreness [9–11]. Despite a wealth of evidence examining the RBE of downhill running, important knowledge gaps remain. Specifically, given the suggested mechanisms of the RBE, the potential of downhill running to evoke improved running energetics in the subsequent bout has been seldom explored, where current evidence is specific to a single study. Khassetarash et al. [11] examined the effects of repeated bouts of 30 min−20% gradient downhill running on the energetic cost of 5 min level running immediately following the damaging exercise bout.˙VO2and the energetic cost of running were unaffected immediately after the downhill running exercise, whilst˙VE was decreased.˙VO2measured during subsequent 5 min level running bouts 24 and 48 h following the downhill running trial was reduced following the second bout, which was attributed to attenuated muscle damage. Whilst these data offer valuable insights, the current understanding of the effect of the RBE on the physiological demand of running is limited to short-duration level running, and effects on longer-duration activity, crossover effects to downhill running, and the consideration of undulating running terrains are yet to be examined and are explored in the current study. Developing this understanding is important in understanding the conditioning potential of downhill running for evoking an improved distance running performance. Furthermore, previous research evaluating acute responses and the RBE of downhill running is specific to long-duration protocols (typically 30 min or greater [1]), and the impact of shorter-duration downhill running, which may be practically more advantageous for athlete conditioning, is yet to be explored. As such, the present study evaluated the effect of repeated bouts of level and downhill running on physiological markers of effort and exercise-induced muscle soreness in trained female distance runners. It was hypothesised that conditioning evoked by the

[1]), and the impact of shorter-duration downhill running, which may be practically more advantageous for athlete conditioning, is yet to be explored. As such, the present study evaluated the effect of repeated bouts of level and downhill running on physiological markers of effort and exercise-induced muscle soreness in trained female distance runners. It was hypothesised that conditioning evoked by the first bout of exercise would reduce˙VO2, RER, HR, BLa, and RPE in the repeated bout of level and downhill running and attenuate post exercise muscle soreness.

Sports2024,12, 169 3 of 12 2. Materials and Methods To complete this experimental study, participants were asked to attend the human performance laboratory at the host institute on three separate occasions, abstaining from intense physical activity in the 48 h prior. In the first visit, the participants completed a graded incremental exercise test to determine their VO 2peakand were familiarised with the experimental protocol. In the remaining two visits, the participants completed the experimental protocol, with each visit separated by three weeks. Prior to each session, the participants were asked to complete a departmental health screen questionnaire. The participants were asked to abstain from strenuous physical activity 72 h following each visit and all experiments were conducted at the same time of day to control forcircadian effects. 2.1. Participants Following ethics approval (Ref: P127140) and the completion of informed written consent, trained female distance runners (Tier 2 in accordance with the classification criteria outlined by McKay et al. [17]), with a minimum of two years’ experience, were recruited from the university running club and running clubs local to the host institute. One par- ticipant dropped out due to illness and another due to reasons not stated, leaving a total sample of 10. The participants were competitive distance runners, were all apparently healthy (determined by completion of the Physical Activity Readiness Questionnaire), and had been injury-free for a minimum of 6 months. The participants had not previously performed prolonged downhill running, but were familiar with treadmill running at level and positive gradients. Those with experience of downhill running, who were not tier 2 competitiveathletes, and who were not injury-free or had a health contradiction prevent- ing safe completion of the physical tasks were excluded. The participant characteristics are reported in Table. Table 1.Participant characteristics. Age (years) 24.4 ±2.0 Height (cm) 164.7 ±1.5 Body mass (kg) 56.2 ±1.8 ˙VO 2peak(mL kg −1 ·min −1 ) 52.9±1.1 70% v˙VO 2peak(km·h −1 ) 8.8±1.4 1500 m PB time (min) 5.1 ±0.4 5 km PB time (min) 21.48 ±1.4 10 km PB time (min) 44.43 ±3.3 Data represented as mean±standard error of mean (SEM); n

Table 1.Participant characteristics. Age (years) 24.4 ±2.0 Height (cm) 164.7 ±1.5 Body mass (kg) 56.2 ±1.8 ˙VO 2peak(mL kg −1 ·min −1 ) 52.9±1.1 70% v˙VO 2peak(km·h −1 ) 8.8±1.4 1500 m PB time (min) 5.1 ±0.4 5 km PB time (min) 21.48 ±1.4 10 km PB time (min) 44.43 ±3.3 Data represented as mean±standard error of mean (SEM); n = 10: 70% vVO 2peak= Velocity at 70%˙VO 2peak; PB = Personal Best data obtained from 2.2. Graded Incremental Exercise Test and Familiarisation Initially height (cm) was measured using a stadiometer (Model 220, Seca, Hamburg, Germany), and body mass (kg) was measured by digital floor standing scales (Model 770, Seca, Hamburg, Germany). Following 10 min of seated rest and a standardised warm- up consisting of 5 min running at 7 km·h −1 , followed by a series of upper and lower body dynamic stretches, the participants completed a˙VO 2peaktest, where the participants were asked to compete a ramp test protocol until volitional exhaustion on a motorised treadmill (HP cosmos Saturn, HP Cosmo Sports & Medical GmbH, Nussdorf-Traunstein, Germany). Starting at 6 km·h −1 , the velocity was increased by 1 km·h −1 every 2 min. Throughout the test, expired gas was measured using a Metalyser (Cortex Metalyser 3B, Cortex Biophysik, Leipzig, Germany), which was calibrated in accordance with the manufacturer’s instructions prior to each test. Heart rate (HR) was continually monitored using a chest-fitted telemetric HR monitor (Polar FT1, Kempele, Finland), and Rating of Perceived Exertion (RPE 6–20 scale) was measured using the Borg scale. Within the first minute following the completion of the test, blood lactate (BLa) concentration was determined by means of a finger prick capillary sample. Initially, the finger was wiped with

Sports2024,12, 169 4 of 12 an isopropyl alcohol swab (Medlock Medical, Oldham, UK), punctured using a1.8 mm lancing device (Safety Lancet, Sarstedt, Germany), and the initial blood was wiped away with a tissue. A 0.7µL sample was collected and BLa determined using a Lactate Plus Meter (Nova biomedical, Waltham, MA, USA).˙VO 2peakwas determined as a Respiratory Exchange Ratio (RER) over 1.1, BLa greater than 8 mmol/L −1 , HR±10 beats of predicted maximal (220-age), and RPE greater than 17, where all conditions were met. RER was averaged over the final 60 s of the final stage, and HR and RPE were recorded at volitional exhaustion. After a period of recovery (~20 min), the participants were asked to complete a 5 min trial of level running followed by a 5 min trial of downhill running at the velocity and gradient to be used in the experimental trial. This served as a familiarisation with the running tasks to be completed in the experimental protocol. 2.3. Experimental Protocol The experimental protocol was completed in accordance with that outlined in Figure. Following 10 min of seated rest, BLa, HR,˙VO2, and RER evaluated from measurements of expired gas were determined in the manner previously described. Upon completion of the standardised warm-up, the participants completed six alternate 5 min trials of level and downhill running, each separated by 2 min standing passive rest. Previous work typically employed a single-effort 30 min trial of downhill running [1]. Given that such long durations of downhill running cause substantial muscle damage and impaired function, a shorter trial of downhill running was selected for the present study, which may be practically more advantageous for athlete conditioning. Furthermore, this protocol was selected to examine the crossover potential of the RBE on multiple trials of level and downhill running.Sports 2024, 12, x FOR PEER REVIEW 5 of 13 recovery period was afforded between bouts and is in keeping with the timeframe used in previous work that has demonstrated RBE-induced neural and biomechanical changes in gait [11,22]. Assessments took place within the competitive season, however, in the pe- riod between bouts participants were

multiple trials of level and downhill running.Sports 2024, 12, x FOR PEER REVIEW 5 of 13 recovery period was afforded between bouts and is in keeping with the timeframe used in previous work that has demonstrated RBE-induced neural and biomechanical changes in gait [11,22]. Assessments took place within the competitive season, however, in the pe- riod between bouts participants were asked to abstain from competition but maintain nor- mal training. Figure 1. Schematic of experimental protocol. Star = 2-min rest; BLa = Blood lactate; RPE = Rating of Perceived Exertion. 2.4. Statistical Analysis Statistical analysis was performed using SPSS v.28 (SPSS Statistics for Windows, IBM Corp, Armonk, NY, USA) and graphical representation using GraphPad Prism v.9 (GraphPad Software, Boston CA, USA). All data are presented as mean ± standard error of mean (SEM). Shapiro–Wilk and visual inspection of Q-Q plots indicated that the data were approximately normally distributed, justifying the application of parametric statis- tical tests. In order to evaluate parity in starting conditions, between-bout differences in the resting physiological variables (V̇ O 2, HR, BLa, and RER) were assessed using a paired samples t-test. V̇ O 2, HR, BLa, RER, and RPE measured during the exercise trials were an- alysed using three-factor repeated measures Analysis of Variance (ANOVA) with Bout (1 vs. 2), Gradient (level vs. downhill), and Trial (1 vs. 2 vs. 3) as factors. Perception of pain was analysed using two-factor repeated measures ANOVA with Bout (1 vs. 2) and Time (immediately post vs. 24 h post vs. 48 h post vs. 72 h post) as factors. Where applicable, Greenhouse–Geisser, recognised as a more conservative epsilon correction, was used to correct the degrees of freedom for the F-distribution on occasions when sphericity was violated. To provide context for the magnitude of any differences found, effect size calcu- lations appropriate to each statistical test were performed. For ANOVA, partial eta squared (ηp 2 ) was calculated to estimate effect sizes and were classified as small (<0.05), moderate (0.06–0.137), or large (>0.138) (Cohen, 1988) [23]. Where applicable, significant main effects and interactions were explored using Bonferroni-corrected pairwise Figure 1.Schematic

for the magnitude of any differences found, effect size calcu- lations appropriate to each statistical test were performed. For ANOVA, partial eta squared (ηp 2 ) was calculated to estimate effect sizes and were classified as small (<0.05), moderate (0.06–0.137), or large (>0.138) (Cohen, 1988) [23]. Where applicable, significant main effects and interactions were explored using Bonferroni-corrected pairwise Figure 1.Schematic of experimental protocol. Star = 2-min rest; BLa = Blood lactate; RPE = Rating of Perceived Exertion. In accordance with previous literature examining the physiological and biomechanical effects of downhill running, for downhill trials participants ran at a gradient of−15% [18,19]

Sports2024,12, 169 5 of 12 and at the velocity that represented 70% of the velocity achieved at˙VO 2peak[19,20]. Five- minute trials represent the minimum time required to see a plateau in expired gas outcome measures [18]. From expired gas,˙VO2and RER were averaged over the final 60 s of each trial, and HR and RPE were recorded in the final 30 s of each trial. Two-minute rest intervals between trials were used to measure BLa and change the gradient of the treadmill. Upon completion of the test, the participants were allowed to walk or run at a self-selected pace for 5 min. Immediately upon completion of the treadmill running protocol, the participants were asked to evaluate their regional perception of muscle soreness using a modified version of the Talag [21] 0–6-point scale, anchored at one end with a score of “0—No discomfort” and at the other “6—Unbearable Pain”. Participants completed three sets of 10 squats, and upon completion of each set, completed the perception of pain scale focused separately on the gastrocnemius, quadriceps, hamstrings, and gluteal muscles. An average of the three scores for each muscle/muscle group was recorded. This procedure was repeated 24, 48, and 72 h following, and participants were asked to abstain from intense physical activity during this period. These procedures were repeated in the second experimental trial, which occurred a minimum of 3 weeks later. Evidence suggests that the RBE can last up to 6 months [16], however, the time course of the RBE elicited from downhill running is yet to be explored and there is little consensus in the literature regarding the most suitable time to complete the second bout. Typically, previous work has separated bouts by periods ranging from 5 daysto 5 weeks [1]. Given that following eccentric exercise, the restoration of muscle force generating ability can take 7–14 days [15], a 3 week recovery period was afforded between bouts and is in keeping with the timeframe used in previous work that has demonstrated RBE-induced neural and biomechanical changes in gait [11,22]. Assessments took place within the competitive season, however, in the period between bouts

The study investigates the physiological effects of downhill running on trained female distance runners.