The Effects of Resistance Training on Road Cycling Performance Among Highly Trained Cyclists: A Systematic Review

Abstract

Yamamoto, LM, Klau, JF, Casa, DJ, Kraemer, WJ, Armstrong, LE, and Maresh, CM. The effects of resistance training on road cycling performance among highly trained cyclists: a systematic review. J Strength Cond Res 24(2): 560-566, 2010-Highly trained cyclists may be hesitant to incorporate resistance training (RT) with their endurance training (ET) because of the mixed data regarding concurrent RT and ET (CT). The purpose of this review was to search the scientific body of literature for randomized controlled trials (RCTs) of CT on road cycling performance for highly trained cyclists. Key words (including cycling and strength training) were used to search relevant databases through September 2009 for literature related to CT. Randomized controlled trials were included if they scored ≥5 on the Physiotherapy Evidence Database scale. Five studies met the inclusion criteria: highly trained road cyclists (>7 h·wk⁻¹ or > 150 km·wk⁻¹, with at least 6 months of training), outcome measure was cycling performance (time trial or time to exhaustion), and RT performed off-bike. Two of the 5 studies found no improvement in performance with CT, but these studies added RT on top of the athletes' existing ET. The 3 studies with improved cycling performance replaced a portion of the athletes' ET with RT, and 2 of the 3 studies included high-intensity explosive-type resistance exercises. Despite the limited research on CT for highly trained cyclists, it is likely that replacing a portion of a cyclist's ET with RT will result in improved time trial performance and maximal power.

Introduction

Cyclists commonly implement resistance training (RT) programs in an effort to improve performance. Concurrent resistance and endurance training (CT) can impede optimal strength development (^17,18); however, the same may not be true of endurance performance. Combined resistance and aerobic training repeatedly improved measures of strength and endurance in untrained individuals, likely because of increased overall fitness (¹²). For well-trained endurance road cyclists, it is less certain if improvements in strength from RT result in improved performance such as time trials (TT) of varying distances, time to exhaustion (TTE), or 1-hour cycle tests (OHT) (⁵).

Initial gains in muscle strength because of RT can be attributed to neuromuscular adaptations, such as improved motor unit recruitment and synchronization, and improved force development rate, not muscle hypertrophy (³). Positive muscular adaptations associated with hypertrophy include increased anaerobic enzyme activity, increased force production, increased intramuscular glycogen, or shifts within major fiber type groups. It may be that years of intensive endurance training (ET) induce neuromuscular adaptations that increase muscle fiber recruitment and spread their power production over a larger area of active muscle during pedaling (¹⁵), producing the same results as off-bike RT. It is unknown if these adaptations are induced by factors other than high-mileage cycling or if off-bike RT would enable cyclists to reduce their on-road training volume and/or improve their performance. Regardless of how these improvements are achieved, elite cyclists want to induce these positive adaptations to sustain attacks, climb hills, or sprint in the final segment of a race. Concurrent RT and ET with highly trained distance runners demonstrated improved running economy or running performance (²²). The same may be true for highly trained road cyclists.

Endurance athletes are often hesitant to incorporate RT into their regimen because of fears of negative effects of hypertrophy on capillary density and mitochondrial function (¹¹); however, several researchers have found no negative change in maximal oxygen uptake (o₂max) from RT (¹¹). Furthermore, it is possible that RT could attenuate the loss of type I muscle fibers and connective tissue (²¹) and help stave off future injury. Increased capillary and mitochondrial density and oxidative enzyme activity are associated with increased endurance performance, but poorly planned CT can work at cross-purposes to each other (⁴).

To give cyclists evidence-based advice on RT through the manipulation of the acute program variables (¹⁰), we undertook a systematic review of the existing CT literature for trained cyclists. We hoped to see if consensus exists regarding off-bike, weight-bearing RT, and road cycling performance. Cyclists and coaches have strong opinions regarding the use of RT regardless of evidence in the literature. Using best practices in cycling training would enable athletes to maximize their potential with an optimal volume of training and would help eliminate myths and antiquated methods that persist among riders even at the highest level of the sport. The purpose of this study was to search the body of scientific literature for original research addressing the effects of RT on endurance road cycling performance in highly competitive cyclists to establish a baseline of understanding of CT for both coaches and researchers.

Methods

We searched MEDLINE, Sport Discuss, ProQuest Dissertations and Theses databases, and Journal of Strength and Conditioning archives through September 2009 using the string “(cycling or bicycling) AND (strength training OR resistance training OR weight lifting OR weightlifting) NOT (respiratory muscles OR obese OR obesity OR stroke).” Inclusionary and exclusionary criteria used to narrow the focus of this review are listed in Table 1. Resistance training was defined as noncycling, weight-bearing, or weight-loaded activity including free weight and machine exercises. The subcategories for RT included circuit training (a series of free weight and/or machine exercise performed one after another with minimal rest between exercises), heavy weight training (dynamic constant external RT with exercises such as back squat and bench press), and explosive strength training (plyometric or stretch-shortening cycle exercises).

Table 1: Inclusionary and exclusionary criteria.*

We identified articles specific to measures of cycling performance with RT with elite athletes. All randomized controlled trials (RCTs) assessing the affects of RT on endurance and road cycling performance were initially examined (Figure 1). All articles were read, and the outcomes of each article were recorded. The references of all identified articles were also examined to identify additional articles that would be eligible for this review. The majority of the examined articles did not meet inclusionary criteria (review articles or training studies for untrained or recreationally trained active subjects) and were excluded from analysis; however, they were retained for review and discussion.

Figure 1: Criteria for selection of articles for review.

All included articles were ranked using the Physiotherapy Evidence Database (PEDro) scale (²⁰). The PEDro scale was developed for the PEDro by the Centre for Evidence Based Physiotherapy as a checklist to examine and rate internal validity (randomization; allocation; similarity of key measures at baseline; and blinding of subjects, therapists, and assessors) and interpretability (between group statistics, descriptions of point measures, and measure of variability). The 11-item scale yields a maximum score of 10 if all criteria are satisfied. For this review, a minimum inclusionary score was 5.

We chose the PEDro scale because it has tested reliability and was developed to evaluate RCTs. Although we did not examine physiotherapy, the similarity of the type of trials warrants the use of the PEDro scale. Maher et al. (¹⁶) found interclass correlations of 0.56 for total score for individual ratings and 0.68 for panel ratings.

Two reviewers independently evaluated each of the 5 articles that met inclusionary criteria using the PEDro scale. Scores were recorded, and full consensus was achieved over the scores given to the 5 articles. A third reviewer was not needed as a tiebreaker to resolve differences in scores. The kappa value for all 5 RCTs was 1.0 (perfect agreement).

Resistance training studies with highly trained road cyclists do not score high with the PEDro scale because of the difficulty blinding allocation, treatment, and assessment. Future researchers could increase their PEDro score by stating concealment of allocation and by blinding assessors to the groups to which subjects were allocated.

Data Synthesis

PEDro scores for the 5 selected articles ranged from 5 to 6 of 10 possible points. PEDro scores do not always reflect a well-designed study because points are not awarded when participants are not blinded to their assignment. It is impossible to blind subjects and therapists in training studies but blinding of assessors may be possible. Random assignment to control or training group is required to eliminate the potential for skewed results. The training protocols are not commensurate, so they cannot be directly compared with each other, but we can assess whether the participants improved performance and whether it seems likely that the results can be extrapolated to similar athletes.

The studies by Bishop et al. (²) and Hickson et al. (⁸) both scored 5 of 10 on the PEDro scale. Random allocation of the subjects into training groups was not specified. The PEDro scores for the other 3 articles were 6 of 10 (^1,9,19). The difference in scores does not diminish the quality of the studies by Bishop et al. (²) or Hickson et al. (⁸) because concealment of allocation may not be relevant to training studies because with proper supervision and training, one subject is no more likely to improve than another. Additionally, blinding of subjects and therapists is not possible, although future studies may consider blinding assessors. Tables 2 and 3 show PEDro scores and summaries of each summary. Results of the 5 studies were mixed and reported either increased performance or no difference between resistance-trained and control groups.

Table 2: Reviewed articles.*

Table 3: Description of experimental and control group training.*

Bastiaans et al. (¹) replaced a portion of the experimental group's ET with high-repetition, low-weight, explosive RT over 9 weeks. Subjects completed resistance exercises as explosively as possible, and weight was adjusted to maintain the speed of movement during the first 20 repetitions with some power loss during the last 10 repetitions. Resistance-trained subjects increased power output during as OHT, which correlated with a 7.1% increase in maximal power output. Total volume of training (h·wk⁻¹) was not different between the experimental and control groups, but 37% of the experimental group's training volume was RT.

Bishop et al. (²) implemented a 12-week periodized program with heavy back squats only. Although 1 repetition maximum (1RM) improved, OHT performance did not. The experimental group completed this RT program in addition to their ET and reported no difference in total ET volume than the control group.

Hickson et al. (⁸) trained 8 subjects on a regimen of strength training 3 days per week for 10 weeks. Although all subjects were endurance-trained athletes, they were not all trained cyclists. The training protocol involved cycling several times each week, and cycling was tested. Overall, the subjects increased strength 30% for the squat and knee extension and flexion. Cyling TTE increased 20% with no negative effects on cycling performance with the addition of RT, particularly on short-term endurance.

Jackson et al. (⁹) compared both high resistance (H-Res) and high repetition (H-Rep) to endurance only training. The H-Res group added 4 × 4 squat, leg curl, leg press, and single-leg step-ups at 85% 1RM to their ET, whereas the H-Rep group completed the same exercises but with a volume of 2 × 20 at 50% 1RM. Despite significant strength gains in both experimental groups, neither showed increased TTE.

Paton and Hopkins (¹⁹) replaced 12 ET sessions over 5 weeks with high-intensity, explosive-type resistance exercises. Subjects completed 12 × 30-minute sessions that combined explosive weighted exercises with on-bike, short-interval (5 × 30 seconds), high-intensity sprints. Improved exercise efficiency and anaerobic threshold result in greater gains in 1 km and 4 km TT performance (i.e., sprint and endurance performance) than control subjects.

Discussion

The current body of scientific literature on CT for elite cyclists shows mixed results for improved performance. Elementary heavy weight RT programs added on top of an athlete's current ET volume does not improve performance in trained cyclists likely because it is not sport specific and because the added training volume results in fatigue (^2,9). It is reasonable to conclude from the limited evidence available that explosive training with 30-40% 1RM resistance benefits the performance of trained cyclists.

Despite our best efforts to give evidence-based recommendations on CT for improved road cycling performance, this systematic review does have its limitations. The small number of RCT that met our inclusion criteria limits our discussion to a relatively limited range of RT programs, but this does emphasize the fact that CT is implemented by coaches with little empirical evidence. Furthermore, the RT programs used may not have been ideally designed with attention to periodization or the incorporation of Olympic style lifts.

The 2 studies that showed no benefit to RT for elite cyclists added the RT program on top of the ET program (^2,9), whereas the 3 studies showing improved performance replaced a portion of the subjects' ET volume with RT (^1,8,19). It is possible that these high-level athletes could not maintain the increased training volume for 10-12 weeks, and fatigue or over-training compromised any benefits that may have been conferred from the RT. Additionally, neither Bishop nor Jackson incorporated explosive RT into their programs (^2,9). Bastiaans suggested that performance was unchanged in the Bishop study because the training was traditional “slow” RT (¹). It may also be that Bishop's periodized RT program consisted only of back squats with varied sets and repetitions and was not designed with sport-specific goals. Jackson et al. (⁹) emphasized the importance of maintaining a sustainable training volume, which could be a limiting factor in improved performance because neither Bishop's nor Jackson's experimental groups experienced a decrement in aerobic performance (^2,9). Paton replaced a portion of the cyclists' ET volume, whereas others (¹⁹), such as Hickson et al. (⁸), added RT to the subjects' existing training volume, thus increasing the overall training volume.

Paton found that a combination of explosive and heavy RT improved 1 km and 4 km TT performance (¹⁹), but it is impossible to separate the performance improvements attributed to on-bike explosive training and off-bike RT. However, Paton was the only researcher to use a TT as a performance measure (¹⁹). The other studies used OHT, TTE, or short-term performance as outcome measures (^1,2,8,9). Although these performance results are easily comparable in the laboratory setting, only the TT for a set distance is applicable to cycling competition.

It is important to note that the 3 studies with improved performance included explosive resistance exercises into their training programs, and 2 of the 3 replaced a portion of the ET volume with RT. The 2 studies that reported no change in performance used elementary training programs and added these programs to preexisting training volume.

The short duration of these training studies does not allow for speculation on the effects of long-term cycling-specific RT for trained road cyclists. Additionally, only Paton studied cyclists during a competitive season (¹⁹). The training phase and the RT program are 2 important factors to consider when designing a periodized RT program. Based on this systematic review of the literature, it is reasonable to conclude that cyclists should include an explosive RT program, similar to the protocol in the study by Bastiaans (¹). Coaches, athletes, and researchers speculate on CT programs based on current strength training science. This systematic review creates a baseline of understanding so that as we move forward, we can build on our knowledge base. Future research should focus on the optimal percentage of RT to total training volume, frequency of RT, and the cost to benefit ratio to CT over the course of a season. Furthermore, future research would do well to evaluate performance such as set-distance TT as an endpoint rather than TTE, to determine which RT programs will elicit the greatest performance improvements in sport competition.

Practical Applications

Cyclists are generally concerned with body mass and are often resistant to add RT for fear of increasing their lean body mass, which can hinder hill climbing, and any increased strength would be offset by the decrement in climbing performance on the road. However, current evidence suggests that well-designed RT programs can attenuate the reduction of type I muscle fibers and connective tissue (¹¹). Although the body of evidence is limited, the authors recommend replacing a portion of an athlete's ET volume with explosive RT to increase TT performance and maximal power output and to minimize the risk of fatigue from an overwhelming total training volume.

The current RT paradigm focuses on sport-specific training to improve performance. A thorough understanding of the acute program variables (¹⁰) and the size principle (^6,7) are of utmost importance when designing a RT program for highly trained road cyclists. Coaches and researchers designing future studies should use this systematic review as a starting point to design protocols that implement RT programs that emphasize heavier weight with low repetitions, Olympic style lifts, and plyometrics to increase force production and improve performance.