Abstract
ffects of concurrent strength and endurance training have been well studied in untrained and moderately-trained individu- als. However, studies examining these effects in individuals with a long history of resistance training (RT) are lacking. Additio n- ally, few studies have examined how strength and power are af- fected when different types of endurance training are added to an RT protocol. The purpose of the present study was to compare the effects of concurrent training incorporating either low-volume, high-intensity interval training (HIIT, 8-24 Tabata intervals at ~150% of VO 2max) or high-volume, medium-intensity continuous endurance training (CT, 40-80 min at 70% of VO 2max), on the strength and power of highly-trained individuals. Sixteen highly- trained ice-hockey and rugby players were divided into two groups that underwent either CT (n = 8) or HIIT (n = 8) in parallel with RT (2-6 sets of heavy parallel squats, > 80% of 1RM) during a 6-week period (3 sessions/wk). Parallel squat performance im- proved after both RT + CT and RT + HIIT (12 ± 8% and 14 ± 10% respectively, p < 0.01), with no difference between the groups. However, aerobic power (VO 2max) only improved after RT + HIIT (4 ± 3%, p < 0.01). We conclude that strength gains can be obtained after both RT + CT and RT + HIIT in athletes with a prior history of RT. This indicates that the volume and/or intensity of the endurance training does not influence the magni- tude of strength improvements during short periods of concurrent training, at least for highly-trained individuals when the endur- ance training is performed after RT. However, since VO 2max im- proved only after RT + HIIT and this
athletes with a prior history of RT. This indicates that the volume and/or intensity of the endurance training does not influence the magni- tude of strength improvements during short periods of concurrent training, at least for highly-trained individuals when the endur- ance training is performed after RT. However, since VO 2max im- proved only after RT + HIIT and this is a time efficient protocol, we recommend this type of concurrent endurance training. Key words: Endurance, exercise; HIIT, performance, resistance, squat. Introduction Performance in most sports depends on the interplay be- tween several physiological factors. A challenge for coaches and athletes is to find the right combination and work load of exercises during training to promote a long- term optimization of all these factors. This is an important part of the periodization process, which is the division of training into phases with different objectives to promote performance and to avoid excessive fatigue and overtrain- ing (Smith, 2003). Even though the objective during one such phase could be strength improvements via resistance training (RT), most athletes need to simultaneously train other physical capacities to avoid a decline in performance. Combining resistance and endurance exercises is espe- cially challenging because several studies have shown that muscle hypertrophy and gains in strength and power are often blunted when endurance exercises are added to a RT program (Bell et al., 2000; Dudley and Djamil, 1985; Fyfe et al., 2016; Hakkinen et al., 2003; Hickson, 1980; Kraemer et al., 1995; Sale et al., 1990). The mechanisms underpin- ning this interference effect are not well understood but likely comprise a combination of factors affecting both acute and chronic fatigue as well as the exercise induced anabolic response (Coffey and Hawley, 2017). Examples of such factors may include reduced neural activation; ac- cumulation of metabolites such as inorganic phosphate, H + and ammonia; and depletion of ATP, creatine phosphate and muscle glycogen (Leveritt et al., 1999). Power is the feature most negatively affected by concurrent training, and studies show that just a few rela- tively short endurance sessions per week are enough to blunt power (Hakkinen et
include reduced neural activation; ac- cumulation of metabolites such as inorganic phosphate, H + and ammonia; and depletion of ATP, creatine phosphate and muscle glycogen (Leveritt et al., 1999). Power is the feature most negatively affected by concurrent training, and studies show that just a few rela- tively short endurance sessions per week are enough to blunt power (Hakkinen et al., 2003; Mikkola et al., 2012). Muscle hypertrophy and strength seem to be less nega- tively affected, and a low-to-moderate volume endurance training (2–3 sessions/wk, 20–60 min/session) is associ- ated with no or only minor blunting effects (Hakkinen et al., 2003; Lundberg et al., 2013; Shaw et al., 2009; Tsitkanou et al., 2016). However, even minor blunting ef- fects may be detrimental for elite athlete performance, and moreover, if long and/or frequent endurance sessions are added to a RT program there is a large body of evidence showing that muscle hypertrophy and strength will be com- promised (Hickson, 1980; Jones et al., 2013; Kraemer et al., 1995). For example, Hickson (1980) observed a strong blunting effect on one-repetition maximum (1RM) squat progression when running exercises (40 min, 6 ses- sions/wk) were added to a 10-week RT program. In recent years, high-intensity interval training (HIIT) has become a very popular form of endurance train- ing among both athletes and recreationally-active individ- uals. The popularity of HIIT can be attributed to the fact that it is time efficient and provides performance and health improvements that are similar to those gained from more traditional low/medium-intensity, long-duration continu- ous training (Francois and Little, 2015; Gibala et al., 2006; Milanovic et al., 2015). Since it is well established that high-volume endurance training has a negative impact on muscle hypertrophy, strength and power (Hickson, 1980; Jones et al., 2013; Kraemer et al., 1995), HIIT might be a better choice during training periods when these outcomes need to be prioritized. However, a potential problem with the HIIT approach is that even if the duration is short, the high intensity of this training might have a negative impact on strength and power due to its potential peripheral fatigu-
et al., 2013; Kraemer et al., 1995), HIIT might be a better choice during training periods when these outcomes need to be prioritized. However, a potential problem with the HIIT approach is that even if the duration is short, the high intensity of this training might have a negative impact on strength and power due to its potential peripheral fatigu- ing effect. This is supported in acute studies where HIIT Research article
Concurrent training, highly trained individuals 168 performed prior to RT reduced force generating capacity and RT volume (Bentley et al., 2000; de Souza et al., 2007). The mechanisms behind this effect is not well known but altered neuromuscular recruitment patterns, accumulation of metabolites and reduced substrate availability have been suggested (Ratamess et al., 2016). Interestingly, a recent study examining the long term effect of concurrent training did not find a larger attenuating effect of HIIT compared with moderate-intensity continuous training on strength and power gains (Fyfe et al., 2016). Therefore, reducing training volume rather than intensity seems more important for avoiding the potential interfering effects of concurrent training. Most concurrent training interventions have been studied in untrained or moderately-trained individuals. In- dividuals with long-term experience in strength and power training might respond differently to the addition of endur- ance training to their routine. Therefore, the objective of the present study was to examine the effects of two differ- ent concurrent training programs on strength and power gains in individuals with a long history of RT. We hypoth- esized that the addition of high-volume CT to a six-week RT program would have a blunting effect on strength and power compared to the effect of low-volume HIIT. Methods Participants Sixteen male former high-level athletes (ice-hockey and rugby players, 27.3 ± 5.0 years) participated in the study. They were still active athletes who trained regularly but competed sporadically. The participants were considered for inclusion if they were 1) currently undergoing strength training four times or more per week, 2) had more than five years of experience with regular strength training, and 3) included squats in their weekly training routine. The par- ticipants were considered to be highly-trained based on their long history of elite-training and excellent perfor- mance in the 1RM parallel squat exercise (1.7 ± 0.3 kg / kg body mass), which was in line with that of international rugby players and power athletes (Baker and Newton, 2008; Zourdos et al., 2016). The participants were assigned to groups that performed either squat RT followed by CT (RT + CT; n = 8)
elite-training and excellent perfor- mance in the 1RM parallel squat exercise (1.7 ± 0.3 kg / kg body mass), which was in line with that of international rugby players and power athletes (Baker and Newton, 2008; Zourdos et al., 2016). The participants were assigned to groups that performed either squat RT followed by CT (RT + CT; n = 8) or squat RT followed by HIIT (RT + HIIT; n = 8). The exercise order, i.e. performing RT first, was based on previous findings that sequencing strength training prior to endurance training appears to be beneficial for lower body strength gains (Murlasits et al., 2018). The two groups were matched for 1RM squat strength and VO 2 max . Two subjects, one in the RT + CT group and one in the RT + HIIT group, interrupted their training and were ex- cluded from the study. The participants were instructed to maintain their normal diet throughout the intervention, to record food in- take during the 24 h preceding the pre-tests, and to dupli- cate the same diet before post-tests. Performance enhanc- ers such as caffeine and creatine, as well as alcohol, were not allowed during the intervention period. The participants were informed about the possible risks and discomforts involved before giving their written consent to participate in the study. The study was approved by the Regional Ethics Committee of Stockholm, Sweden. Testing Pre- and post-tests were performed in a rested state (no training > 48 h before the tests) and at the same time of day for each subject. Four familiarization sessions were per- formed before the pre-tests, which included both heavy parallel squats and HIIT on a cycle ergometer. The test or- der was as follows: anthropometric measurements (weight, height and body fat), counter-moment-jump vertical height (CMJ), 1RM parallel squat, maximal lactate steady-state workload (MLSS) and VO 2max (Haff and Triplett, 2016). The duration of all the tests performed in one session was ~2 h. Body fat was calculated from skinfold thickness measured with calipers (Harpenden, Baty International CTD, West Sussex, UK) as described by Durnin and Womersley (1974).
height and body fat), counter-moment-jump vertical height (CMJ), 1RM parallel squat, maximal lactate steady-state workload (MLSS) and VO 2max (Haff and Triplett, 2016). The duration of all the tests performed in one session was ~2 h. Body fat was calculated from skinfold thickness measured with calipers (Harpenden, Baty International CTD, West Sussex, UK) as described by Durnin and Womersley (1974). CMJ test The participants performed a general warm-up before test- ing that consisted of light cycling at 100 W for 8 min. CMJ performance was then assessed using an optical measure- ment system (Optojump, Microgate, Bolzano-Bozensh, It- aly). The system has been demonstrated to have a strong validity and test-retest reliability for the estimation of ver- tical jump height (Glatthorn et al., 2011). The participants performed three maximal unloaded jumps with 30 s of pas- sive recovery between each effort. If the third jump was higher than the previous two, the subject performed an ad- ditional fourth jump. If this effort was higher than the third a fifth jump was added, and so on, until no further improve- ments were observed. The best jump was used to determine maximal vertical jump height. Jumps were initiated from a standing starting position, with the hands placed on the hips throughout the jump. The jump depth was self-selected, and the participants were instructed to accelerate as quickly as possible from their lowest position to achieve maximal jump height. 1RM parallel squat test Lower-body strength was assessed via 1RM testing using the parallel-back squat exercise. The participants per- formed five warm-up sets as follows: 10 repetitions at 20 kg, 5 repetitions at 40% of predicted 1RM, 5 repetitions at 60% of predicted 1RM, 3 repetitions at 80% of predicted 1RM, and 2 repetitions at 90% of predicted 1RM. The rest periods between the sets were 2, 3, 3 and 5 min, respec- tively. The participants then performed sets of 1 repetition of increasing weight to determine their 1RM. Five minutes of rest were provided between each attempt. The partici- pants were required to reach a parallel thigh/floor position or deeper for the attempt to
90% of predicted 1RM. The rest periods between the sets were 2, 3, 3 and 5 min, respec- tively. The participants then performed sets of 1 repetition of increasing weight to determine their 1RM. Five minutes of rest were provided between each attempt. The partici- pants were required to reach a parallel thigh/floor position or deeper for the attempt to be considered successful, as determined by two test supervisors (certified strength and conditioning specialists). An attempt was deemed success- ful only when the two supervisors reached consensus. MLSS and VO 2 max tests MLSS was determined during incremental submaximal ex- ercise (5 min of cycling, 90 RPM, at each step: 100, 150, 200, 250 W, etc. until reaching a Borg scale score ≥ 17). The participants completed 4–6 steps, such that the total duration of the test was ≤ 30 min. Capillary blood samples
Petre et al. 169 were collected from the fingertip during the 1-min periods of rest between each step and analyzed for lactate using an automated analyzer (Biosen 5140, EKF Diagnostics, Bar- leben, Germany). The gas composition of expired air and HR were measured continuously using the Oxycon Pro (Er- ich Jaeger GmbH, Hoechberg, Germany) and Polar Electro Oy (Kempele, Finland) systems, respectively. MLSS was determined based on the D max method as previously de- scribed (Cheng et al., 1992). The submaximal MLSS test was followed by 10 min of pedaling at 100 W before the VO 2 max test was initiated at a workload corresponding to the last completed 5-min step of the MLSS test. Thereafter, the workload was increased by 20 W each minute until fa- tigue was reached (drop in cadence to < 50 RPM). VO 2 max was calculated as the highest recorded mean oxygen uptake during the last 60 s of the test. The criteria for attaining VO 2 max (RPE ≥ 18, RER ≥ 1.1, and a plateau in VO2 with increasing workload) were met for all participants. Time to exhaustion during the VO 2 max test (TTE-VO2 max) was de- fined as the time point when the cadence involuntarily dropped to below 50 RPM. A capillary blood sample was collected immediately after the test to measure peak lactate levels (BL-VO 2 max). The Oxycon Pro system used for the gas exchange measurements is known for its high validity and reliability (Foss and Hallen, 2005). Training The training interventions lasted 6 weeks and the partici- pants performed 3 concurrent strength and endurance workouts per week, i.e. for a total of 18 training sessions. No additional lower body strength or endurance training was allowed. Three subjects had to perform 1-2 additional training sessions during week 7 to reach a total of 18 ses- sions, giving a training compliance of 100%. All exercise sessions were supervised by members of the investigative team who were certified strength and conditioning special- ists. Each strength training session was initiated with 10- min cycling at 100 W, followed by 4 sets
had to perform 1-2 additional training sessions during week 7 to reach a total of 18 ses- sions, giving a training compliance of 100%. All exercise sessions were supervised by members of the investigative team who were certified strength and conditioning special- ists. Each strength training session was initiated with 10- min cycling at 100 W, followed by 4 sets of parallel squats with a light to medium loading (40–80% of 1RM). There- after the participants performed 5x2 reps, ≥ 90% 1RM (Mondays and Fridays) or 2x5 reps, ≥ 80% 1RM (Wednes- days) of parallel squats. The loading was self-selected (above 90% respectively 80% of 1RM) and all sets were performed to failure or close to failure. If the first set/sets were not close to failure the loading was increased. Three minutes of rest was allowed between light to medium load- ing sets and 5 min between heavy loading sets. Approxi- mately 15 min after the strength training session, the RT + CT group performed 40–80 min of continuous cycling (Monark 828 E, Monark Exercise, Varberg, Sweden), and the RT + HIIT group performed 4–20 min of high-intensity interval cycling (Monark Ergometic, Peak Bike 894 E, Monark Exercise, Varberg, Sweden). The duration of the CT sessions was increased from 40 min during weeks 1–2 to 60 min during weeks 3–4 and 80 min during weeks 5–6. The intensity was set to 70% of VO 2 max and was kept con- stant throughout the intervention. The HIIT protocol was increased from one block of eight Tabata intervals (8 × 20 s separated by 10 s rest) during weeks 1-2 to two blocks during weeks 3-4 (2 × 8 × 20 s) and three blocks during weeks 5–6 (3 × 8 × 20 s). The intensity was set to 150% of VO 2 max during the first training session; if a participant was able to complete all intervals, a 10-W increase was added during the following session. The RT + HIIT group, there- fore, experienced a progression in both duration and inten- sity, whereas the RT + CT group experienced a progression
20 s). The intensity was set to 150% of VO 2 max during the first training session; if a participant was able to complete all intervals, a 10-W increase was added during the following session. The RT + HIIT group, there- fore, experienced a progression in both duration and inten- sity, whereas the RT + CT group experienced a progression in duration only. Statistical analyses Data are presented as the mean ± SD. Repeated-measures analysis of variance (2 × 2 mixed ANOVA) was used to test the interaction between time (pre- and post-training) and intervention (RT + CT and RT + HIIT group). Within- group differences were assessed using paired t-tests. The effect size (ES) was calculated as the mean difference be- tween the pre-training and the post-training values divided by the standard deviation of the pre-training values. The following scale was used to categorize the magnitude of effect as proposed by (Rhea, 2004) for highly-trained indi- viduals: < 0.25 = trivial; 0.25-0.5 = small; 0.5-1.0 = mod- erate; > 1.0 = large. Statistical significance was determined at p < 0.05. All statistical analyses were performed using STATISTICA (StatSoft, Inc, Tulsa, Oklahoma, USA). Results Body composition Body mass and lean body mass increased slightly in the RT + HIIT group (1.3 ± 1.4%, p = 0.035 and 1.2 ± 1.3%, p = 0.032 respectively) whereas only lean body mass increased in the RT + CT group (1.2 ± 1.5%, p = 0.044) (Table 1). The percent body fat remained unchanged in both groups. Figure 1. Effect of 6 weeks of training on leg strength (1RM in parallel squats). Values are reported as the mean ± SD. RT + CT: resistance training followed by continuous endurance training (n = 8); RT + HIIT: resistance training followed by high-intensity interval training (n = 8). **p < 0.01 vs. pre-training. Strength and CMJ performance Maximal strength, measured as 1RM for parallel squats, increased in both the RT + CT group (11.5 ± 7.8%, p = 0.006) and the RT + HIIT group (14.4 ± 10.1%, p = 0.001) (Figure 1). The effect size
+ HIIT: resistance training followed by high-intensity interval training (n = 8). **p < 0.01 vs. pre-training. Strength and CMJ performance Maximal strength, measured as 1RM for parallel squats, increased in both the RT + CT group (11.5 ± 7.8%, p = 0.006) and the RT + HIIT group (14.4 ± 10.1%, p = 0.001) (Figure 1). The effect size was moderate for both groups (0.75 and 0.66 respectively). CMJ vertical height was un- affected by training in both groups (RT + CT: 41.4 ± 4.5 cm pre-training and 40.1 ± 4.1 cm post-training, p = 0.15; RT + HIIT: 40.6 ± 6.2 cm pre-training and 40.7 ± 4.8 cm post-training, p = 0.89).
Description
This research investigates concurrent training effects on strength and power in highly-trained athletes.