Contralateral Asymmetry in Cycling Power Is Reproducible and Independent of Exercise Intensity at Submaximal Power Outputs

he purpose of the current investigation was to examine the effects of exercise intensity on asymmetry in pedal forces when the accumulation of fatigue is controlled for, and to assess the reliability of asymmetry outcomes during cycling. Participants completed an incremental cycling test to determine maximal oxygen consumption and the power that elicited maximal oxygen consumption (pVO 2max). Participants were allotted 30 min of recovery before then cycling at 60%, 70%, 80%, and 90% of pVO 2max for 3 min each, with 5 min of active recovery between each intensity. Participants returned to the laboratory on separate days to repeat all measures. A two-way repeated measures analysis of variance (ANOVA) was utilized to detect differences in power production AI at each of the submaximal exercise intensities and between Trials 1 and 2. Intraclass correlations were utilized to assess the test–retest reliability for the power production asymmetry index (AI). An ANOVA revealed no signi cant intensity–visit interactions for the power production AI (f = 0.835,p= 0.485,h 2= 0.077), with no signi cant main effects present. ICC indicated excellent reliability in the power production AI at all intensities. Exercise intensity did not appear to affect asymmetry in pedal forces, while excellent reliability was observed in asymmetry outcomes. Keywords:asymmetry; cycling; pedaling; pedal forces; power 1. Introduction Asymmetry (i.e., signi cant differences between contralateral limbs) in

= 0.835,p= 0.485,h 2= 0.077), with no signi cant main effects present. ICC indicated excellent reliability in the power production AI at all intensities. Exercise intensity did not appear to affect asymmetry in pedal forces, while excellent reliability was observed in asymmetry outcomes. Keywords:asymmetry; cycling; pedaling; pedal forces; power 1. Introduction Asymmetry (i.e., signi cant differences between contralateral limbs) in physiological tness components and contribution during bipedal movements has gained interest and has been widely investigated [1,2]. It has been noted that signi cant asymmetry for force production capabilities between the lower limbs has been associated with decrements in physical performance. Speci cally, asymmetry in the force production of the lower limbs has been associated with reduced jump height and slower change of direction speed times [3,4]. Additionally, a strong focus has been placed on injury risk and occurrence in association with asymmetry [5]. Asymmetries > 15% have been associated with increased injury incidence in both athletic and non-athletic populations [5–8]. These results suggests that a reduction in asymmetry would be bene cial for enhancing performance and reducing injury risk. Success in the sport of cycling is highly dependent upon the ability to generate and maintain sustained power outputs [9]. Thus, pedaling in a manner that maximizes the transfer of force into power production is of vital importance to cyclists. Asymmetry in force, torque, and power production have all been reported during cycling, with varying degrees of asymmetry reported [2,10–12]. Exercise intensity has been identi ed as a factor that in uences the manifestation of asymmetry during cycling [11,13]. However, previous protocols have not accounted for the accumulation of fatigue during continuous incremental cycling tests or time trials. Previous investigations have reported signi cant increases in asymmetries in counter-movement jumps following repeated sprints, or during soccer Symmetry2023,15, 1142.

Symmetry2023,15, 1142 2 of 9 matches [14,15]. It is unclear what degree of asymmetry will be present during cycling when the accumulation of fatigue is controlled for. Another key limitation in asymmetry research in general is a lack of reporting on the reliability of asymmetry outcomes [1]. This likely results in an assumption of the reliability of the asymmetry outcome, and an inability to determine the true degree of asymmetry [1,16]. Thus, the purpose of the current investigation was (1) to evaluate the effects of exercise intensity on pedal force asymmetries during bouts of submaximal cycling separated by periods of recovery to counteract the potential in uence of the accumulation of fatigue, and (2) to determine the test–retest reliability of pedal force asymmetries. Submaximal exercise intensities were chosen for investigation to re ect the reported intensities within which cyclist accumulate the most time during races (~83% of total race time below VT2/LT2) [17]. Based on a previous investigation, it was hypothesized that pedal force asymmetries would not be statistically signi cantly different at different exercise intensities, and good- to-excellent test–retest reliability would be observed for pedal force asymmetries [12]. 2. Materials and Methods All participants completed two separate laboratory visits separated by at least 48 h but no more than one week. Visit 1 consisted of anthropometric measures, and an incremental cycling test (ICT) to determine the maximal oxygen consumption (VO2max) and the power which elicited VO2max (pVO2max). Both VO2max and pVO2max were con rmed with a square wave bout veri cation protocol following the ICT. Participants then completed 4–3 min bouts of submaximal cycling at 60%, 70%, 80%, and 90% of pVO2max in a ran- domized order, with 5 min of recovery between each bout. Asymmetry in pedal forces was assessed during each of the 3 min bouts of submaximal cycling. All procedures were repeated upon Visit 2 to assess the reliability of the pedal force asymmetry measures. 2.1. Participants Eleven subjects (nine males and two females) were recruited for this investigation, all with 2 years of experience in cycling training and racing. Those with a previous history of

was assessed during each of the 3 min bouts of submaximal cycling. All procedures were repeated upon Visit 2 to assess the reliability of the pedal force asymmetry measures. 2.1. Participants Eleven subjects (nine males and two females) were recruited for this investigation, all with 2 years of experience in cycling training and racing. Those with a previous history of lower limb orthopedic injuries or procedures (e.g., arthritis, hip replacement, or knee surgery) that could in uence asymmetry outcomes were excluded. This study was approved by the Texas State University institutional review board, and each subject gave verbal and written informed consent prior to participation, in accordance with the Code of Ethics of the World Medical Association (the Declaration of Helsinki). All testing was conducted in a climate-controlled laboratory at a temperature of 20 to 22 C. 2.2. Methodology Subjects were instructed to abstain from eating, caffeine ingestion, and exercise two hours, 12 h, and 24 h, respectively, prior to each visit. A magnetically braked cycle ergometer (Sport Excalibur, Lode; B.V. Medical Technology, Croningen, The Netherlands) with built-in modi ed strain gauges within each crank arm was used for both ICTs and all bouts of submaximal cycling. The height and fore/aft positions of the seat and handlebars of the cycle ergometer were adjusted to each subject's comfort, and were recorded for replication on subsequent visits. The self-reported physical activity rating (PA-R) scale was used to determine initial workload of the ICT and subsequent increases in workload [18,19]. Brie y, PA-R is a 16 point scale describing levels of physical activity over the previous 6 months, with 0 being “avoid walking or exertion” and 15 being “run 50 miles or more per week or spend 13 h or more per week in comparable physical activity” [18,19]. PA-R, age, body mass index (BMI), and sex were plugged into an equation to estimate VO2max and peak power output (PPO), with PPO then divided by the desired number of stages for the ICT [19]. The current ICT used one-minute stages, with workloads designed to induce task failure within 10 stages. Task failure was de

in comparable physical activity” [18,19]. PA-R, age, body mass index (BMI), and sex were plugged into an equation to estimate VO2max and peak power output (PPO), with PPO then divided by the desired number of stages for the ICT [19]. The current ICT used one-minute stages, with workloads designed to induce task failure within 10 stages. Task failure was de ned as a >10 revolution per minute (rpm)

Symmetry2023,15, 1142 3 of 9 decrease from preferred cadence for >5 s despite strong verbal encouragement. PPO was determined using the following equation [20]: PPO = Wcom + (t/60 WLI) where Wcom is the workload, in watts (W), for the nal fully completed stage;tis the time, in seconds, that the nal uncompleted stage was sustained; 60 is the duration, in seconds, for each stage; and WLI is the workload increment in W. A square wave bout veri cation protocol was used to verify VO2max and determine the power that elicited VO2max (pVO2max) [21]. Immediately upon reaching task failure for the ICT, participants began 3 min of active recovery at 50 watts (W), and then proceeded to cycle at their preferred cadence at 105% of PPO until reaching task failure again. Inspired and expired gases were collected and analyzed via a metabolic cart (True One 2400; Parvo Medics, Sandy, UT, USA) throughout the ICT and square wave bout veri cation to deter- mine VO2max. Gases were collected breath-by-breath and analyzed via 20 s averages. The highest 20 s average from either the ICT or square wave bout veri cation was de ned as VO2max, with the associated workload identi ed as pVO2max. Subjects were allotted 30 min of rest after completing the ICT and square wave bout veri cation. During this time, subjects were allowed to drink water ad libitum. Subjects then began cycling for 5 min at 50 W, serving as their warm-up. Subjects then completed 4–3 min bouts of cycling at 60%, 70%, 80%, and 90% of pVO2max in a randomized order, separated by 5 min of active recovery at 50 W. Subjects were blinded to the workload and were instructed to maintain the same preferred cadence from the ICT throughout the submaximal bouts of cycling. Methods for assessing pedal force asymmetries have been described previously [12]. Brie y, the independent modi ed stain gauges within each crank arm were calibrated prior to each use, so that strain gauges detected no forces while unloaded. Pedal force data were collected and analyzed using Lode Ergometry Manager (version 10. Lode: B.V.

ICT throughout the submaximal bouts of cycling. Methods for assessing pedal force asymmetries have been described previously [12]. Brie y, the independent modi ed stain gauges within each crank arm were calibrated prior to each use, so that strain gauges detected no forces while unloaded. Pedal force data were collected and analyzed using Lode Ergometry Manager (version 10. Lode: B.V. Medical Technology, Croningen, The Netherlands), with the amount of power generated during the crank cycle that resulted in forward propulsion reported as power in watts (W). Forces were collected independently for each lower limb and denoted as preferred (PL) or non-preferred limb (NPL) based on subjects response to the validated question “If you were to shoot a ball at a target, which leg would you use to kick the ball?”, with the subjects' response recorded as theirPL[8]. It has been recommended to use the terminology “preferred” rather than “dominant” when referring to a subjectively preferred limb for completing a task [22]. An asymmetry index (AI) was calculated for power production using the following equation: AI(%) = PL NPL (PL+NPL)/2 100 AI values of 100 and 100 indicate 100% contribution from theNPLandPL, re- spectively. AnAIof zero indicates equal contribution of both limbs [10,12]. A threshold of 10% forAIhas previously been used to establish the presence of asymmetry for pedal forces during cycling [10,12]. 2.3. Statistical Analysis All analysis was conducted using IBM SPSS Statistics (version 26.0; IBM Corp., Ar- monk, NY, USA). Demographic data were summarized with descriptive statistics. Paired sample t-tests were used to assess signi cant difference in VO2max and pVO2max between Visits 1 and 2. Intraclass correlation coef cients (ICCs) were utilized to assess the test–retest reliability for the power production AI. ICCs were interpreted as having poor, good, and excellent reliability with coef cients of <0.4, 0.4 to 0.75, and >0.75, respectively [1,23]. Abso- lute reliability was evaluated using the coef cient of variation (CV) and the standard error of the measurement (SEM). A two-way repeated measures analysis of variance (ANOVA) was utilized to detect differences in the power production AI at each of the submaximal

good, and excellent reliability with coef cients of <0.4, 0.4 to 0.75, and >0.75, respectively [1,23]. Abso- lute reliability was evaluated using the coef cient of variation (CV) and the standard error of the measurement (SEM). A two-way repeated measures analysis of variance (ANOVA) was utilized to detect differences in the power production AI at each of the submaximal

Symmetry2023,15, 1142 4 of 9 exercise intensities, and between Visits 1 and 2. Post hoc analysis was performed when appropriate, to identify signi cant differences. Effects sizes for the ANOVA were analyzed when appropriate using eta squared (n 2 ), with values of 0.02, 0.13, and 0.26 indicative of small, medium, and large effect sizes, respectively [24]. 3. Results The subjects' age, height and body mass (mean standard deviation) were observed to be 35.1 16.5 years, 174.9 7.0 cms, and 72.5 15.9 kgs, respectively. Paired sample t-tests revealed no statistically signi cant differences in VO2max (53.3 12.0 mL/kg/min vs. 52.2 12.2 mL/kg/min) and pVO2max (349.5 105.4 W vs. 341.0 101.8 W) between Visits 1 and 2. Only 10 of the 11 participants' data were able to be used to determine VO2max due to one participant experiencing feelings of claustrophobia while wearing the mask used to collect inspired and expired gases during the ICT. Two, four, three, and one participants were classi ed as performance level 1, 2, 3, and 4, respectively, according to Pauw et al.'s guidelines on using the metric of relative maximal oxygen consumption (VO2max) assessed during the investigation [25]. Power production AI results and reliability data are reported in Table. Power produc- tion AI data were normally distributed. Individual asymmetry index values are illustrated in Figure. ICC results were interpreted as having excellent reliability in the power pro- duction AI at 60%, 70%, 80%, and 90% of pVO2max. The two-way repeated measures ANOVA revealed no signi cant intensity–visit interactions for the power production AI (f = 0.835,p= 0.485,h 2= 0.077), with no signi cant main effects present for intensity (f = 0.270,p= 0.847,h 2 = 0.026) or Visit (f = 0.011,p= 0.919,h 2 = 0.001). Table 1.Asymmetry Index Results and Reliability (n = 11). Variable Visit 1 (Mean SD) Visit 2 (Mean SD) ICC r (95% CI) p CV SEM 60% pVO 2max AI (%) 0.4 13.4 1.3 11.4 0.945 (0.797–0.985) 0.00 612.9 1.9 70% pVO 2max AI (%) 1.3 15.6 0.8 10.3 0.792 (0.223–0.944) 0.01 594.0 4.8 80% pVO 2max AI (%) 1.9 13.8 1.6 9.4

Index Results and Reliability (n = 11). Variable Visit 1 (Mean SD) Visit 2 (Mean SD) ICC r (95% CI) p CV SEM 60% pVO 2max AI (%) 0.4 13.4 1.3 11.4 0.945 (0.797–0.985) 0.00 612.9 1.9 70% pVO 2max AI (%) 1.3 15.6 0.8 10.3 0.792 (0.223–0.944) 0.01 594.0 4.8 80% pVO 2max AI (%) 1.9 13.8 1.6 9.4 0.777 (0.118–0.941) 0.02 4267.5 5.46 90% pVO 2max AI (%) 0.1 8.8 2.5 8.3 0.888 (0.604–0.969) 0.00 1404.5 5.51 Abbreviations: pVO2max = power which elicited maximal oxygen consumption, AI = asymmetry index, SD = standard deviation, ICC = intraclass correlation coef cient, CI = con dence interval; CV = coef cient of variation; SEM = standard error of the measurement.Symmetry 2023, 15, x FOR PEER REVIEW 4 of 10 (ANOVA) was utilized to detect differences in the power production AI at each of the submaximal exercise intensities, and between Visits 1 and 2. Post hoc analysis was per‐ formed when appropriate, to identify significant differences. Effects sizes for the ANOVA were analyzed when appropriate using eta squared (n 2), with values of 0.02, 0.13, and 0.26 indicative of small, medium, and large effect sizes, respectively [24]. 3. Results The subjects’ age, height and body mass (mean ± standard deviation) were observed to be 35.1 ± 16.5 years, 174.9 ± 7.0 cms, and 72.5 ± 15.9 kgs, respectively. Paired sample t‐ tests revealed no statistically significant differences in VO 2max (53.3 ± 12.0 mL/kg/min vs. 52.2 ± 12.2 mL/kg/min) and pVO 2max (349.5 ± 105.4 W vs. 341.0 ± 101.8 W) between Visits 1 and 2. Only 10 of the 11 participants’ data were able to be used to determine VO 2max due to one participant experiencing feelings of claustrophobia while wearing the mask used to collect inspired and expired gases during the ICT. Two, four, three, and one par‐ ticipants were classified as performance level 1, 2, 3, and 4, respectively, according to Pauw et al.’s guidelines on using the metric of relative maximal oxygen consumption (VO 2max) assessed during the investigation [25]. Power production AI results and reliability data

wearing the mask used to collect inspired and expired gases during the ICT. Two, four, three, and one par‐ ticipants were classified as performance level 1, 2, 3, and 4, respectively, according to Pauw et al.’s guidelines on using the metric of relative maximal oxygen consumption (VO 2max) assessed during the investigation [25]. Power production AI results and reliability data are reported in Table 1. Power pro‐ duction AI data were normally distributed. Individual asymmetry index values are illus‐ trated in Figure 1. ICC results were interpreted as having excellent reliability in the power production AI at 60%, 70%, 80%, and 90% of pVO 2max. The two‐way repeated measures ANOVA revealed no significant intensity–visit interactions for the power production AI (f = 0.835, p = 0.485, η 2 = 0.077), with no significant main effects present for intensity (f = 0.270, p = 0.847, η 2 = 0.026) or Visit (f = 0.011, p = 0.919, η 2 = 0.001). ‐20 ‐18 ‐16 ‐14 ‐12 ‐10 ‐8 ‐6 ‐4 ‐202468101214161820 90% pVO2max Power Production Asymmetry Index Trial 1 Trial 2 (A) Figure 1.Cont.

Symmetry2023,15, 1142 5 of 9Symmetry 2023, 15, x FOR PEER REVIEW 5 of 10 ‐40 ‐35 ‐30 ‐25 ‐20 ‐15 ‐10 ‐5 0 5 10152025303540 80% pVO2max Power Production Asymmetry Index Trial 1 Trial 2 (B) ‐40 ‐35 ‐30 ‐25 ‐20 ‐15 ‐10 ‐5 0 5 10152025303540 70% pVO2max Power Production Asymmetry Index Trial 1 Trial 2 (C) Symmetry 2023, 15, x FOR PEER REVIEW 6 of 10 Figure 1. Asymmetry index at (A) 90%, (B) 80%, (C) 70%, and (D) 60% power pVO 2max. Table 1. Asymmetry Index Results and Reliability (n = 11). Variable Visit 1 (Mean ± SD) Visit 2 (Mean ± SD) ICC r (95% CI) p CV SEM 60% pVO 2max AI (%) 0.4 ± 13.4 1.3 ± 11.4 0.945 (0.797–0.985) 0.00 612.9 1.9 70% pVO 2max AI (%) 1.3 ± 15.6 − 0.8 ± 10.3 0.792 (0.223–0.944) 0.01 594.0 4.8 80% pVO 2max AI (%) 1.9 ± 13.8 1.6 ± 9.4 0.777 (0.118–0.941) 0.02 4267.5 5.46 90% pVO 2max AI (%) 0.1 ± 8.8 2.5 ± 8.3 0.888 (0.604–0.969) 0.00 1404.5 5.51 Abbreviations: pVO 2max = power which elicited maximal oxygen consumption, AI = asymmetry index, SD = standard deviation, ICC = intraclass correlation coefficient, CI = confidence interval; CV = coefficient of variation; SEM = standard error of the measurement. 4. Discussion The current investigation sought to determine (1) if pedal force asymmetries were statistically significantly different during bouts of submaximal cycling at varying intensi‐ ties separated by periods of recovery, and (2) if test–retest reliability exists for pedal force asymmetries. Based on previous investigations, it was hypothesized that pedal force asymmetries would not be statistically significantly different at different exercise intensi‐ ties, and good‐to‐excellent test–retest reliability would be observed for pedal force asym‐ metries [12]. Based on the current results, both hypotheses were accepted. There have been a number of investigations published on pedal force asymmetries with a focus on the impact of exercise intensity [2,10–12,26,27]. However, with several different devices, outcomes, and methodologies used in the assessment of pedal forces, there have been conflicting results reported. Initially, an inverse association was

This study investigates pedal force asymmetries in cycling across different exercise intensities.