A Comparison of the Effect of Strength Training on Cycling Performance between Men and Women

ing the last decade numerous review articles have been published on how concurrent strength and endurance training affect cycling performance. However, none of these have reviewed if there are any sex differences in the effects of concurrent training on cycling performance, and most research in this area has been performed with male cyclists. Thus, the aim of the current paper is to review the scienti c literature on the effect of concurrent training on cycling performance in male and female cyclists with a special emphasis on potential sex differences. The results indicate that both male and female cyclists experience a similar bene cial effect from concurrent training on cycling performance and its physiological determinants compared to normal endurance training only. Some data indicate that women have a larger effect on cycling economy, but more studies are needed to explore this further. Furthermore, the adaptations to strength training thought to be responsible for the bene cial effects on cycling performance seem to be very similar between men and women. Interestingly, increased muscle cross-sectional area in the main locomotor muscles seems to be an important adaptation for improved performance, and, contrary to popular belief,

but more studies are needed to explore this further. Furthermore, the adaptations to strength training thought to be responsible for the bene cial effects on cycling performance seem to be very similar between men and women. Interestingly, increased muscle cross-sectional area in the main locomotor muscles seems to be an important adaptation for improved performance, and, contrary to popular belief, cyclists should aim for increased muscle cross-sectional area when adding strength training to their normal training. We conclude that both male and female cyclists can improve their cycling performance by adding strength training to their normal training. Keywords: concurrent training; endurance performance; sex differences; muscle strength; muscle hypertrophy; training adaptations 1. Introduction Adding strength training to cyclists normal training has been shown to improve cy- cling performance [1–3], and during the last decade there has been published numerous review articles on the effects of strength training on cycling performance [4–6]. However, none of these have reviewed whether there are any sex differences regarding the effects of strength training on cycling performance. In fact, the literature investigating the effects of adding strength training to the usual training in cyclists is dominated by studies performed on male cyclists. One of the few studies investigating the effect of adding strength training to the usual training of female cyclists reported no bene cial effect on cycling performance in a 1 h time-trial test nor in cycling economy [7]. However, the cyclists in this study performed only one strength training exercise (parallel squats), and this was probably not a suf cient training volume for bene cial effects to occur [8]. A recent study reported improved average power output during and 8-min performance test in trained female cyclists after 6 weeks of either traditional or velocity-based strength training [9]. However, this study did not include a control group only performing endurance training, making it dif cult to assess if the improved performance was because of the strength training per se. Furthermore, to the best of our knowledge, no study has directly compared the effects between men and women in one single study. There are some physiological

strength training [9]. However, this study did not include a control group only performing endurance training, making it dif cult to assess if the improved performance was because of the strength training per se. Furthermore, to the best of our knowledge, no study has directly compared the effects between men and women in one single study. There are some physiological differences between men and women that in theory might lead to different effects of strength training J. Funct. Morphol. Kinesiol.2021,6, 29.

J. Funct. Morphol. Kinesiol.2021,6, 29 2 of 11 on cycling performance. For example, when performing muscle contractions at the same relative intensities, women have been reported to be more resistant to muscle fatigue [10], and during endurance exercise at submaximal intensities, women oxidize proportionally more fat and less carbohydrate and protein than men [11]. Furthermore, endocrine re- sponses differ between men and women in response to exercise [12,13], and the adaptations in the mechanical properties of tendons after strength training are different [14]. Some years ago, we conducted a more thorough investigation on the effects of strength training on cycling performance and performance determinants in female cyclists [2,15]. This study utilized a strength training program, a testing regime, and testing equipment identical to what we used in male cyclists with bene cial effects on cycling performance [1,16,17], making these studies very suitable for comparing the effects between male and female cyclists. To the best of our knowledge, this study is the only study using a strength training program with a suf cient volume and training load to investigate if female cyclists can bene t from strength training. In the current review, we rst present a short summary of the effects of adding strength training to cyclists' normal training regimes regarding cycling performance and performance determinants regardless of sex. Thereafter, we compare these effects between male and female cyclists with an emphasis on our own studies using a similar training program and testing protocol in both male and female cyclists. Finally, we include a review of the adaptations to strength training thought to induce bene cial effects on cycling performance and discuss if these might be different between men and women. 2. The Effects of Strength Training on Cycling Performance and Its Physiological Determinants Cycling performance is determined by several physiological performance determi- nants. The interaction between maximal oxygen consumption (VO2max) and fractional utilization of VO2max(%VO2max) determines the performance VO2, the rate of aerobic metabolism that can be sustained for the duration of a performance test or competition [18]. The cycling economy or ef ciency then determines the power output at

Its Physiological Determinants Cycling performance is determined by several physiological performance determi- nants. The interaction between maximal oxygen consumption (VO2max) and fractional utilization of VO2max(%VO2max) determines the performance VO2, the rate of aerobic metabolism that can be sustained for the duration of a performance test or competition [18]. The cycling economy or ef ciency then determines the power output at a given amount of energy consumption, and these three factors therefore majorly determine the average power output that can be sustained for a certain period of time or distance, a surrogate measure for cycling performance [18]. In the lab, cycling performance is often measured as the average maximal sustainable power output during 20–60 min tests. Multiple studies reported improved cycling performance measured by this method- ological approach after cyclists added heavy strength training (multiple leg exercises with ~4–12 repetitions maximum, for minimum 8 weeks) to their normal training [2,17,19,20]. In contrast, studies that included strength training programs of either short duration, included a low volume of strength training, or used explosive strength training [7,21–23] failed to show improved performance. Since combining heavy strength training with normal endurance training seems to improve cycling performance, it should also improve at least one of the cycling performance determinants. It seems to have neither a positive nor a negative effect on the development of VO2max[2,7,22,24]. When it comes to ef ciency or cycling economy, the ndings are more equivocal. When cycling economy is measured by the traditional method (i.e., short, 3–5 min, submaximal bouts of cycling), no additive effect of strength training has been observed in well-trained and elite cyclists [1,3,17,25]. However, improvements have been shown in moderate trained cyclists [24,26,27]. Interest- ingly, there are indications that heavy strength training improves cycling economy after prolonged submaximal cycling, also in well-trained cyclists, which is especially relevant in road cycling [16]. %VO2maxis ideally measured directly via VO2measurements during a performance test and then expressed as the average VO2during the exercise in percent of VO2max. Only one study on the effects of strength training on cycling performance has measured %VO2maxin this way and reported an improvement after

prolonged submaximal cycling, also in well-trained cyclists, which is especially relevant in road cycling [16]. %VO2maxis ideally measured directly via VO2measurements during a performance test and then expressed as the average VO2during the exercise in percent of VO2max. Only one study on the effects of strength training on cycling performance has measured %VO2maxin this way and reported an improvement after strength training [2]. However, a common way to estimate %VO2maxis to use the percentage of VO2maxat the lactate threshold, and the few studies that have reported the effect of concurrent training on this

J. Funct. Morphol. Kinesiol.2021,6, 29 3 of 11 measurement in cyclists observed no change [2,17,24]. However, these data should be taken with caution as the only study reporting improved %VO2maxmentioned above did not nd a similar effect of strength training on lactate threshold expressed as percent of VO2max[2]. Furthermore, other studies report improved performance without a concomi- tant improvement in VO2maxor cycling economy [1,3] after concurrent training, further supporting the claim that improved %VO2maxcan occur after concurrent training. The ab- solute power output at the lactate threshold is, amongst others, affected by the cycling economy. Therefore, and despite not all studies reporting signi cant improvement in cycling economy, the nding of improved lactate threshold power output in several studies after combined heavy strength- and endurance training is somewhat expected [1,2,17,20,25]. However, there are also studies observing no improvements in power output at a de ned [la - ] [3,23,24]. Another lab measurement that can be interpreted as a performance measurement is the peak minute power output achieved during an incremental cycling test to exhaustion when testing VO2max(Wmax). Wmaxis in uenced by VO2max, cycling economy, anaerobic capacity, and neuromuscular characteristics [28]. Accordingly, Wmaxhas been shown to predict endurance performance in cyclists [29,30] and to distinguish elite cyclists from well-trained cyclists [30]. Concurrent endurance and heavy strength training is reported to increase Wmaxor time to exhaustion at Wmaxin trained to well-trained cyclists [1,17,19,24,31]. Another factor important for the cycling performance in mass start races is the ability to close a gap, break away from the pack, or perform well in the nal sprint [32]. The outcome of these crucial moments is largely decided by anaerobic abilities and the size of the involved muscle mass [33,34]. Based on the bene cial effects of heavy strength training on muscle strength and muscle mass, it is as expected that concurrent training has been reported to improve the ability to generate a high power output for a short period of time [1,2,17]. 3. Sex Difference in the Effect of Strength Training on Cycling Performance Since most studies investigating the effects of strength training on cycling performance

heavy strength training on muscle strength and muscle mass, it is as expected that concurrent training has been reported to improve the ability to generate a high power output for a short period of time [1,2,17]. 3. Sex Difference in the Effect of Strength Training on Cycling Performance Since most studies investigating the effects of strength training on cycling performance include only male cyclists, we performed a study on the effects of strength training on cycling performance and performance determinants in female cyclists [2,15]. The female cyclists in this study performed a strength training program identical to what we previ- ously used to induce bene cial effects on cycling performance in male cyclists [1,16,17]. This strength training program lasted for 11–12 weeks with two sessions per week with a training load of 10-4 RM, including four exercises for the lower body with three sets. Both the men and the women continued their normal endurance training. In both male and female cyclists, cycling performance, measured as the average sustainable power output during a 40-min performance test, increased to the same amount after adding strength training to their normal training (men: 6.0 5.6%, women: 6.4 7.9%,Figure ). The improved performance was not because of increased VO2maxas strength training did not improve VO2maxcompared to control cyclists performing their normal endurance training in either the male or female cyclists. Cycling economy measured by the traditional method (i.e., short, 3–5 min, submaximal bouts of cycling) was improved only in the female cyclists in our studies (Figure), and the percent change between men and women was signi cantly different (p= 0.016). Therefore, it is possible that female cyclists have a larger potential for improving cycling economy than male cyclists by adding heavy strength training to their normal endurance training. On the other hand, the male cyclists were on a somewhat higher performance level and completed more endurance training than the female cyclists (9.9 h vs. 5.1 h per week). It appears dif cult to improve cycling economy in very well-trained cyclists [3]. In fact, improved cycling economy after heavy strength training has also been reported in

normal endurance training. On the other hand, the male cyclists were on a somewhat higher performance level and completed more endurance training than the female cyclists (9.9 h vs. 5.1 h per week). It appears dif cult to improve cycling economy in very well-trained cyclists [3]. In fact, improved cycling economy after heavy strength training has also been reported in male cyclists on a lower performance level [24,26,27]. However, research in very well-trained and elite female cyclists is lacking, and it might be that as for men, they do not see an improved cycling economy after strength training, at least when measured during 3–5 min submaximal bouts of cycling.

J. Funct. Morphol. Kinesiol.2021,6, 29 4 of 11J. Funct. Morphol. Kinesiol. 2021, 6, x FOR PEER REVIEW 5 of 11 and women directly in the same study. However, similar strength training program, test protocols and testing equipment were used alongside a control group. To the best of our knowledge, only one other study investigating the effect on con- current training on cycling performance by comparing a concurrent strength and endur- ance training group to an endurance-training-only group has focused on female cyclists [7]. In this study, well-trained female cyclists added 12 weeks of heavy strength training (parallel squats two times per week) to their normal endurance training but found no ben- eficial effect on cycling performance in a 1-h time-trial test nor in cycling economy [7]. However, this might be because the strength training program only included one strength training exercise, making the total strength training volume too low for beneficial effects to occur [8]. Figure 1. Percent change in physiological measurements and cycling performance after 11–12 weeks of heavy strength training in male and female cyclists. The results from the male cyclists are from [1,16], and the results from the female cyclists are from [2,15]. Values are mean ± SD. RM = repetition maximum, CSA = cross sectional area, VO 2max = maximal oxygen consumption, W max = power output at VO2max, CE = cycling economy, LT = lactate threshold. Note: A negative change in cycling economy indicates reduced VO 2 and improved cycling economy. CE semi fatigued state was measured during the last hour of a 3 h submaximal cycling trial, and the 5-min performance was measured directly following the 3 h trial. The increase in VO 2max in the male cyclists was not different from control male cyclists. 4. Mechanisms behind the Effects of Strength Training on Cycling Performance and Sex Differences in These Mechanisms The proposed mechanisms responsible for improved cycling performance after strength training are summarized in Figure 2. One frequently proposed mechanism for the improved cycling economy often observed after cyclists add strength training to their normal training is a larger contribution of type

cyclists. 4. Mechanisms behind the Effects of Strength Training on Cycling Performance and Sex Differences in These Mechanisms The proposed mechanisms responsible for improved cycling performance after strength training are summarized in Figure 2. One frequently proposed mechanism for the improved cycling economy often observed after cyclists add strength training to their normal training is a larger contribution of type I muscle fibers at a certain power output [4]. Type I fibers have been reported to be more efficient than type II fibers [35,36], and although not an universal finding [37], cycling efficiency has been related to proportions of type I fibers in the active muscles [38–40]. When the maximal muscle strength increases, the force levels required to ride at a certain power output is reduced relatively to maximal force. This implies that the type I muscle fibers can account for a larger proportion of a certain absolute power output [4,19], as follows from the size principle of motor unit re- cruitment [41]. Furthermore, concurrent heavy strength- and endurance training in female athletes has been reported to increase cross sectional area (CSA) of type I muscle fibers Figure 1. Percent change in physiological measurements and cycling performance after 11–12 weeks of heavy strength training in male and female cyclists. The results from the male cyclists are from [1,16], and the results from the female cyclists are from [2,15]. Values are mean SD. RM = repetition maximum, CSA = cross sectional area, VO 2max= maximal oxygen consumption, Wmax= power output at VO 2max, CE = cycling economy, LT = lactate threshold. Note: A negative change in cycling economy indicates reduced VO 2and improved cycling economy. CE semi fatigued state was measured during the last hour of a 3 h submaximal cycling trial, and the 5-min performance was measured directly following the 3 h trial. The increase in VO 2maxin the male cyclists was not different from control male cyclists. We measured %VO2maxwith VO2measurements during the 40-min performance test in the female cyclists and found an improvement from 78.9% to 82.2% of VO2max. Unfortunately, we did not perform this measurement in the

trial, and the 5-min performance was measured directly following the 3 h trial. The increase in VO 2maxin the male cyclists was not different from control male cyclists. We measured %VO2maxwith VO2measurements during the 40-min performance test in the female cyclists and found an improvement from 78.9% to 82.2% of VO2max. Unfortunately, we did not perform this measurement in the male cyclists; however, the im- proved 40-min performance in the male cyclists compared to the male control cyclists with similar changes in VO2maxand cycling economy indicate an improved %VO2max. Similar ndings have also been reported in other elite male cyclists [3]. This study found an 8% increase in the average power output during a 45-min performance test with no changes in cycling economy and VO2maxafter young elite cyclists added strength training. The authors calculated that the average power output during the 45-min test increased from 76% to 83% of the power output corresponding to 100% of VO2maxafter the strength training intervention. Therefore, it appears that both male and female cyclists improve %VO2maxafter a period of heavy strength training. It might be speculated that the male cyclists increased their %VO2maxmore than the female cyclists, since the improvement in 40-min performance test was similar despite only the female cyclists improved cycling economy (Figure). However, this might also be explained by the increase in VO 2max in the male cyclists (similar in both control and strength training group). It is therefore unknown if there are sex differences in the improvement of %VO2maxafter concurrent training. The power output at lactate threshold improved similarly in both sexes after strength training (men: 4.1 5.1%, women: 7.6 12%,p= 0.39, Figure). To simulate a typical mass start race in cycling, we performed a test consisting of a 3 h submaximal cycling trial (at the same absolute power output pre and post) directly followed by a 5-min performance test with the aim of highest possible power output during the 5-min test. The results were similar between the male and female cyclists [15,16]. Both had reduced oxygen consumption and hence improved cycling economy during the last part of the submaximal

The study compares strength training effects on cycling performance in men and women.