LFHV strength training has been reported to elicit improvements in HIEE and LIEE performance (59,74,85); however, research conclusions are mixed (7,45,60) (Table 2). Paavolainen et al. (59) found that LFHV strength training (<40% 1RM) improved 5k run time, running economy, VMART, 20-m sprint speed, and distance covered on a 5-jump test in male cross-country runners (
Considering that gaining body mass is a concern for endurance athletes, one of the purported benefits of LFHV strength training is the lower degree of muscle hypertrophy compared with HFLV strength training (28,70), but still being able to achieve increases in strength. In addition, increased muscle fiber cross-sectional area (CSA), maximal strength, and power output can be diminished or fully blunted by concurrent strength and endurance training with the degree of decrement depending on the mode, frequency, and duration of endurance training (2,14,34,42). Rønnestad et al. (64) found that increased CSA of the quadriceps muscle was associated with increased peak power output and cycling time trial performance after combined heavy strength training (twice/week, 3 × 4–10RM) and endurance training in well-trained cyclists without a noticeable change in body mass (64). Therefore, altering the strength to body mass ratio should be more of a concern for endurance athletes than body mass alone. Furthermore, although increases in “nonfunctional” hypertrophy may be detrimental to performance (3,86,91), increases in task specific hypertrophy may be an important factor in enhancing endurance performance, as the typical ectomorphic endurance athlete is unlikely to gain significant amounts of hypertrophy through strength training (89).
It has been suggested that LFHV strength training may provide an additive effect to those elicited by HFLV strength training on HIEE and LIEE performance (85). Taipale et al. (85) tested this hypothesis by dividing endurance runners into 3 groups (LFHV, HFLV, combination) and found no differences between groups in measures of strength (1RM), power (CMJ height), and endurance performance (85). Considering there is a delay between when a training stimulus is implemented and the subsequent effects on performance (90), a sequenced approach may be more appropriate than trying to improve strength, power, and endurance simultaneously (15,81).
The primary goals of any successful training program are to reduce the likelihood of injury and optimize performance (81). Before designing a training program, however, the coach and the athlete must understand that training is a comprehensive process that harmonizes a myriad of factors to foster athlete development. Figure 1 depicts some of these factors that affect athletic performance. Therefore, the sport coaches, strength and conditioning staff, and sports medicine professionals each play an important role within their own disciplines to contribute to an athlete's development. In addition, the management of external stressors in the athlete's daily life is also an important component in the optimization of performance. To achieve this objective, however, training variables must be integrated in a sequence over the course of the training process (79). The training process is traditionally organized into 3 basic levels: macrocycles, mesocycles, and microcycles (79). A macrocycle is a long-duration training cycle, typically classified as 12 months of training, which are composed of multiple mesocycles. Mesocycles are moderate-length periods of training, which can focus on developing specific fitness characteristics within the macrocycle. Finally, each mesocycle is composed of shorter training periods referred to as microcycles (79). The tool used to structure each phase of training within a macrocycle is referred to as an “annual training plan” (15).
More specifically, the annual plan is a long-term training template used to guide the coach and athlete in the design and implementation of various training phases (15). The annual training plan can be separated into phases: the general preparatory phase, competitive phase, peak phase, and active rest (Figure 2). For a detailed description of each phase, the reader is encouraged to examine the work of Bompa and Haff (15).
To reduce the likelihood of injury and maximize athletic performance, strength and conditioning professionals should organize training adaptations in a logical manner to minimize fatigue and highlight technical and fitness characteristics (e.g., strength, speed, endurance, etc.) at precise times of the training year “to increase the potential to achieve specific performance goals” (79). This process of chronologically manipulating physiological adaptations is referred to as periodization. Although varying definitions of this term have been proposed, periodization has been most recently defined as, “The strategic manipulation of an athlete's preparedness through the employment of sequenced training phases defined by cycles and stages of workload” (22). Furthermore, if the training stimuli are sequenced appropriately, each phase of training will enhance or “potentiate” the next training phase (15,79,81). This concept, referred to as phase potentiation, is essential in the development of endurance-specific performance characteristics.
The development of high-power outputs and high RFDs are vital to success in most sporting events (76) and can differentiate levels of athletic performance (5,6,29). Maximal power output and RFD have conventionally been viewed as fitness characteristics that are less important for endurance sports. This is misguided, however, because there is evidence indicating that average power output over the course of a long-distance race and maximal power output during the final sprint may be critical factors determining the outcome of the event (56,58,80).
Although there are a number of schematics to choose from when manipulating these variables, a traditional model fits the previously described sequence of strength and power development (79,81). During the general preparation phase, higher volumes of strength training should be used to enhance work capacity and increase lean body mass (15). Despite concerns over increases in body mass, for many endurance athletes, the general preparation phase is one of the few times during the annual plan where small increases in muscle hypertrophy can be achieved. This in turn will potentiate gains in maximal strength and power in subsequent phases of training. As the athlete progresses from the general preparation period to the specific preparation and competition phases of the macrocycle, strength training volume is progressively diminished while training intensity increases, as strength and power become the primary fitness characteristics of interest, respectively (38). Before a culminating event in the competitive season (e.g., championship race), the peaking phase or taper requires “a reduction of the training load during a variable period of time, in an attempt to reduce the physiological and psychological stress of daily training and optimize performance” (53). After the peaking phase, the athlete transitions into the off-season with a period of active rest consisting of recreational activities in which both intensity and volume are reduced and recovery is the objective (81).
The selection of appropriate training volumes and intensities within each training phase is vital in the facilitation of the desired physiological response. For endurance athletes with limited strength training experience, a traditional model is appropriate (79,81). These athletes should begin with building a neuromuscular base using HFLV strength training, and after a certain strength level is achieved, LFHV strength training can then be implemented (10). This is supported by evidence indicating that among well-trained athletes, LFHV is necessary to make further alterations in the high-velocity end of the force-velocity curve (30,77). Thus, HFLV and LFHV strength training are both important components in the endurance athlete's strength and conditioning program provided they are included at the appropriate time and in the correct sequence (Figure 2).
Regarding high-level endurance athletes, however, the use of a traditional model with a single peaking phase is often impractical, as most athletes will compete in multiple significant events throughout the course of a competitive season. Accordingly, manipulating volume and intensity to produce specific physiological adaptations must coincide with this competitive schedule (80). Unlike the traditional model, after the athlete completes the peaking phase and competes in a key event of the season, further planning will be necessary to prepare the athlete for future competitions of importance (80,81). More specifically, if adequate time exists before the next major event, strength training volume may be increased to re-establish strength levels (63,79). Conversely, if time is insufficient, strength training volume should be increased cautiously to avoid undue fatigue before the next contest (63,80,81).
When selecting exercises for specific phases of training, it is important for practitioners and athletes to consider the transfer of training effect. That is, the degree of performance adaptation that can result from a training exercise (11,81). Therefore, choosing exercises with similar movement patterns and kinetic parameters (e.g., peak force, RFD, acceleration, etc.) will result in a greater transfer to performance (11). Although some endurance sport movements have both closed and open kinetic chain sequences, in movements such as running, closed kinetic chain exercises should be prioritized as they have been suggested to require greater levels of intermuscular coordination (76) and result in greater performance enhancement compared with open chain movements (62,75). Traditional squatting and weightlifting movements are primary examples. Moreover, squat strength has been strongly correlated to athletic movements that require relatively high-velocity, high-power outputs and RFD (6,18). Weightlifting exercises and their derivatives have also shown a strong transfer of training to such movements as well (4,16,37). Practically, these exercises may assist with passing an opponent, enhancing movement economy, increasing average power output, and sprinting the final 100 m of a race (56,58,80). Considering the essential role that these exercises play in the development of strength and power and subsequent effects on HIEE and LIEE, squatting and weightlifting movements should be staples throughout the training year for endurance athletes.
Previous research on concurrent training for endurance athletes suggests that maximum strength is associated with endurance factors, a relationship that is likely stronger for HIEE activities than for LIEE. HFLV strength training can affect increases in HIEE and LIEE through increasing peak force and RFD. LFHV strength training has also been reported to elicit improvements in HIEE and LIEE performance, however, not all studies agree. When considering findings from studies examining changes in endurance performance and related measures after strength training, it seems that concurrent HFLV strength and endurance training may provide superior results compared with LFHV strength and endurance training for relatively weak endurance athletes. For endurance athletes with more strength training experience, a sequenced approach (e.g., block periodized model) may be more appropriate than trying to improve strength, power, and endurance simultaneously.
A limitation to the current research exists in the design and implementation of training protocols. Some studies comparing different strength training modalities fail to control for differences in strength and endurance training volume between experimental conditions. Another limitation, only controlled for in a few studies, is the addition of strength training without a simultaneous reduction in the volume of endurance training. Practically, if applied in an athletic setting, this could result in poor fatigue management and an increased risk of overtraining syndrome. The implementation of an annual training plan where endurance and strength training variables are carefully manipulated will maximize athletic performance while reducing injury risk by more appropriately managing training volume. Future research should examine the effectiveness of monitoring programs in determining when to manipulate training variables throughout a macrocycle and the subsequent effects on endurance performance.
The authors thank Jacob Goodin for his corrections and editorial comments in preparation of this article.
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