Over the years, the number of healthy older individuals practicing sport activities has markedly increased. This growth leads to a considerable increment of master athletes who perform at a high level for their age category (10). In particular, master endurance athletes (i.e., >35 years of age) represent the largest proportion of participants in marathon competitions, and their participation in these events has dramatically increased over the past decades (22). In fact, these athletes train and compete regularly, following detailed and structured training schedules even though they do not have the same technical support in terms of training and recovery. This is because, compared with younger athletes, they have to train between very busy schedules because of work or family duties. Nevertheless, these athletes are capable of (a) remarkable athletic and physiological functional performances (43), (b) training and competing regularly in long distance events and, in some cases, (c) improving the performance achieved at a younger age. This is because the peak exercise performance for age category seems to increase continuously each year (43) despite the well-documented decrease in endurance performance that occurs with age. In fact, loss in performance ability shows a slow but progressive decline from the ages of 30 to about 60 years (10). After that, a progressively steeper decrease is seen (43) even in athletes who are able to maintain sufficient training volume and intensity.
Several studies have reported that regular endurance training throughout the lifespan brings to half the decline in maximal aerobic capacity as seen in sedentary individuals (35). Endurance-running events are strongly related to physiological determinants such as maximal aerobic capacity (V[Combining Dot Above]O2max), running economy (RE), and the exercise intensity at which a high fraction of the V[Combining Dot Above]O2max can be sustained (15). Particularly, the decrease in V[Combining Dot Above]O2max and the reduction in lactate threshold appear to contribute to the decline in endurance exercise performance from young adulthood to early middle age (43). Further, RE is defined as the V[Combining Dot Above]O2 required at a given absolute exercise intensity. Therefore, runners with a better RE use less O2 than runners with a poor RE do at the same running speed (6). Accordingly, RE seems to be a better predictor of endurance performance than maximal oxygen uptake (37) and does not seem to change with advancing age (8). Moreover, it has been suggested that there is a relationship between neuromuscular characteristics and RE (i.e., the more “economical” an individual, the higher the level of contractile strength and muscular stiffness he or she presents) (2). Therefore, strength training programs have received more attention as powerful stimuli to improve mechanical efficiency, muscle coordination, motor unit recruitment patterns (36), and lower limb stiffness regulation with an overall enhancement in the RE. In fact, it has been suggested that an overall increase in the strength parameters can facilitate changes and corrections in the technical model because of an enhancement in the motor unit recruitment (21), especially for individuals who started training at a more advanced age such as Master athletes. Although a combination of strength and endurance training have been advocated for optimal physical function and health in the elderly, most of these studies have been performed on an untrained population (19). Moreover, a number of studies involving young adults have reported impairment in strength development when endurance training is added to a strength training program (19). This potential conflict has been referred to as an “interference phenomenon” because endurance training seems to compromise optimal strength development (17). Nevertheless, studies performed on young trained or even elite athletes do support the contention that concurrent training does not alter the ability to positively adapt to endurance training (11). In fact, strength training for endurance athletes is finalized to optimize their endurance performance. As a consequence, the use of concurrent strength and endurance training in the endurance training periodization has been shown to improve performance in different endurance sports such as crosscountry skiers (18), cyclists (41), and triathletes (33). Concurrent strength and endurance training has also been shown to increase the RE in distance runners (14,21,38,40,46).
Despite the fact that master marathon runners represent the largest proportion of participants in marathon events, studies have been mainly conducted on young or elite athletes, and it is not known if this older athletic population will respond in a similar manner as elite or younger athletes or if including extra training days will induce them to nonfunctional overreaching. Recent evidence (24) suggests that aging affects stress-response signaling. The study demonstrates that after the same resistance training (RT) program, older individuals show no significant increase in myofiber hypertrophy adaptation, whereas younger individuals experience 2 times the growth in type 2 myofibers compared with their older counterparts. Only the younger population was capable of type 1 myofiber growth. Moreover, older individuals have a higher percentage of type 1 muscle fibers and therefore are able to generate less force (23). However, a cross-sectional study on master endurance athletes aged 40–88 years demonstrated that a significant age-associated decline in leg strength and muscle fiber area and type distribution does not appear until after the age of 70 (44).
Therefore, the purpose of this study was to answer the question if incorporating regular strength training on top of the normal running program of Master endurance athletes would be beneficial to RE, as already seen for younger or elite athletes. Our hypothesis is that maximal strength training (MST) or RT added to regular endurance training would lead to different neuromuscular adaptations and consequently different effects on RE in master endurance runners.
Experimental Approach to the Problem
The hypothesis that MST or RT added to regular endurance-running training would lead to different neuromuscular adaptations, and consequently, different effects on RE in master runners was tested. To answer this question, a 6-week training period was chosen because 4- to 8-week cycles of strength training are commonly used in the literature (46), and it was hypothesized that most of the adaptations in RE may occur after 4–6 weeks of strength training (as presented in this study) and that longer protocols may not add further improvements in RE.
Thus, a parallel, 3-group, randomized, longitudinal (pretest-posttest), experimental design was used. To investigate the possible effects of 2 different strength training programs on RE during the preparation of a marathon in Master endurance athletes, anthropometric data, resting metabolic rate (RMR), RE, rating of perceived exertion (RPE), maximal strength (1 repetition maximum [1RM]), squat jump (SJ), countermovement jump (CMJ), and stiffness (STIF) were measured before (at week 0) and after a 6-week strength training program (at week 7). All the subjects performed familiarization trials before the testing days.
Sixteen marathon runners engaged in the same endurance training program were randomly assigned to 1 of the following groups: MST, RT, and a control group (CG). The MST and the RT groups performed RT on top of their normal running program, whereas the CG only performed the normal endurance training regimen. We used as independent variable, the group, whereas the dependent variables were body fat, body mass, 1RM, RMR, CMJ, SJ, and V[Combining Dot Above]O2. The 1RM on leg press has been shown to have high intraclass correlation coefficients (ICCs [0.99]) (28), whereas CMJ and SJ performances show high ICCs (range: 0.997–0.998) for adult male individuals (13). Controlled reliability on RE has been seen indicating that results are relatively stable (37).
Twenty-one master endurance runners from the same running team (5 women and 16 men) were originally recruited to take part in the study and were randomly divided into 1 of the 3 experimental groups (n = 7 per group). The protocol was approved by the University Ethical Committee and the participants gave their written consent before participation. The participants had a history of consistently participating in road races (from 10 km to marathon distance). Five voluntarily discontinued participation and only 16 (12 men and 4 women) completed the 6-week training period. Therefore, the groups were formed as follows (mean ± SD): MST (n = 6; 4 male and 2 female: 44.2 ± 3.9 years, height 170.2 ± 7.6 cm, body mass 71.9 ± 13.1 kg); RT (n = 5; 3 male and 2 female: 44.8 ± 4.4 years, height 170.3 ± 13.8 cm, body mass 67.9 ± 14.7 kg) and a CG (n = 5; 5 male: 43.2 ± 7.9 years, height 175.2 ± 6.9 cm, body mass 71.3 ± 13.7 kg). To prevent potential contaminating effects of the athlete’s ability level and different training schedules, the participants included in this study had to fulfill the following inclusion criteria: (a) be Master athletes (>35 years of age); (b) have at least 5 years of previous endurance training; (c) to be part of the same track and field team followed by the same trainer.
All the tests were performed before and after a 6-week intervention program during the first 6 weeks of their specific 12-week marathon-training program, and measurements were taken before (week 0) and after the strength training interventions (week 7). The tests were separated by a 24-hour resting period. All the tests were performed at the same time of the day ±2 hours in a climate-controlled laboratory (∼21 to 22° C, 53% relative humidity) except for RMR that was performed early in the morning. The participants did not perform any physical activity in the 24 hours resting period and were requested to refrain from using caffeine-containing food or beverages, alcohol, cigarette smoking, or any form of nicotine intake during this period. The subjects were requested to replicate the same food intake before each test. All the subjects performed familiarization trials.
The participants were provided with written and oral instructions before all the testing procedures. The MST and RT program was performed in addition to their regular endurance training, twice a week and before and after the experimental period, RMR, body composition, 1RM, SJ, CMJ, STIF, and an RE test at 3 running speeds were measured (Figure 1). All the tests were randomized; however, the same order was respected in the pretest and posttest for each individual.
Resting Metabolic Rate Measurements
Individuals were asked to refrain from vigorous activity at least 24 hours before the resting metabolic measurements, to eat the same dinner the day before the RMR measurements, and to be 12 hours fasted. They were asked to plan their arrival in the laboratory between 7:00 and 8:30 AM. Pretraining and posttraining measurements were performed at the same time. After 5 minutes of sitting rest, the subjects were fitted with a mask (Fitmate, Cosmed, Rome, Italy) to measure V[Combining Dot Above]O2. Thereafter, they were asked to lie down in a quiet room in a supine position, and a 30-minute habituation period was allowed (34) in a thermoneutral environment (24 ± 0.5° C). The subjects were given 15 minutes to rest, breathing through a mask, during which the RMR was measured. After the RMR measurements, body composition was assessed before and after the training period using the Jackson and Pollock (20) 7-site skinfold equation. Skinfold measurements were taken by the same experienced operator on the right side and recorded to the nearest 0.1 mm using a Lange skinfold caliper (Cambridge Scientific Instrument, Cambridge, MD, USA). Measurements were taken 3 times per site, and the mean value was recorded. Body density was calculated, whereas percent body fat was estimated with the Siri equation (39). Body mass and body height were measured after the RMR test at the same time of the day and under comparable nutritional and training conditions. Body weight and height were measured with a calibrated clinical balance to the nearest gram.
Maximal strength was estimated through the 6RM test on the leg press. All the subjects were positioned on a horizontal leg press (Technogym, Gambettola, Italy) and the knee angle (90°) was fixed to maintain the same position in all test occasions. The athletes were required to perform a 5-minute warm-up period at 40–60% of their maximal predicted 1RM. After a brief recovery period, the athletes were requested to perform the first session with a preliminary load of 15 repetitions. Thereafter, the load was increased every step by 30% until the athlete could not successively complete a 6RM repetition (1). The 1RM was estimated through a conversion table (3). The 1RM was measured at week 0 and after training at week 7. All the tests were performed for each individual at the same time of the day.
All the subjects performed an SJ, CMJ, and an STIF test during the same test day. Each test was separated by a 5-minute rest period. Vertical jump performance was assessed using the SJ and the CMJ tests according to the procedures suggested by Bosco et al. (5). Jumping height was calculated from flight time using kinematic equations (27). Flight time was recorded using an infrared photocell connected to a digital computer (Optojump System, Microgate SARL, Bolzano, Italy). All the tests were performed in a randomized order. For the SJ, the participants were instructed to squat down and hold a knee position (∼90° knee angle) for a few seconds with arms blocked. When cued, the participant was instructed to jump as high as possible. A trial was considered successful when there was no further squatting or countermovement before the execution of the jump. Three trials separated by 1 minute of passive recovery were performed. The best one was recorded for further analysis. To perform the CMJ, the subjects were instructed to start in a standing position with their arms blocked, perform a 2-legged CMJ consisting of a fast downward movement to a freely chosen angle, immediately followed by a fast maximal vertical thrust. Any jump that was perceived to deviate from the required instructions was repeated. Three trials separated by 1 minute of passive recovery were performed. The best one was recorded for further analysis. A multirebound test (7 consecutive jumps) was performed to measure STIF. The participants had 2 trials separated by a 5-minute passive recovery period. The participants were asked to keep their knees as stiff as possible during the test, to jump as high as possible, and to have the shortest contact time. The results from the best trial were used for further analysis. Jumping performance was measured at week 0 and after training at week 7. All the tests were performed for each individual at the same time of the day.
The RE was determined by measuring submaximal V[Combining Dot Above]O2 during 3 different running speeds on a treadmill: 5 minutes at 1 km·h−1 slower than the marathon pace (9.75 ± 1.3 km·h−1), 5 minutes at the marathon pace (10.75 ± 1.3 km·h−1), and 5 minutes at 1 km·h−1 faster than the marathon pace (11.75 ± 1.3 km·h−1) after a standardized warm-up. Before each test, the Cosmed flow meter (Quark b2, Cosmed) was calibrated with a 3-L syringe, and the oxygen analyzer was calibrated with known gas mixtures (16% O2 and 5% CO2) and environmental air (20.9% O2 and 0.03% CO2). During each step, the heart rate was continuously monitored using a heart rate monitor with an internal memory (Polar Team System, Polar, Kempele, Finland), and the subjects were asked to rate their perceived effort according to the rating perceived exertion scale (CR-10 scale) (4) before, at the end of each step, and after exercise. Throughout the tests, the respiratory and pulmonary gas-exchange variables were measured using a breath-by-breath gas analyzer (Quark b2, Cosmed). The RE was defined as the V[Combining Dot Above]O2 determined by averaging the last 2 minutes of each running speed. The RE was measured at week 0 and after training at week 7. All the tests were performed for each individual at the same time of the day.
The subjects were well-trained master runners, who started the season in September 2009 and already participated to different races (10–21 km) in the months before the study (from September to January 2010). The training interventions took place from the beginning of January to Mid-February, and the marathon was scheduled at the end of March. All the subjects were engaged in the same endurance training program that consisted of 4–5 d·wk−1 for a total of 50 km·wk−1 distributed in slow runs, interval training, and tempo runs emphasizing improvement in V[Combining Dot Above]O2max. The subjects were then divided into different strength training protocols while the CG continued only with the regular running program. Resistance was increased every week to maintain the correct number of repetitions per set. The strength training program (Table 1) consisted of 2 training sessions a week and was supervised by a certified fitness instructor. The MST program consisted of 4 sets of 3–4 repetitions of exercises for the lower and upper body at 85–90% of the estimated 1RM. Rest intervals between sets were 3 minutes. The RT included a general conditioning of the main muscle groups of the body and consisted of 3 sets of 10 repetitions at 70% 1RM.
SPSS statistical software (v10.1 for Windows) was used for all statistical analyses. The Kolmogorov-Smirnov test was applied to verify the assumption of normality. One-way analysis of variance (ANOVA) was used to evaluate between-group differences in the dependent variables at pretest. Thereafter, a 1-way ANOVA for repeated measures was used to identify differences between the 3 groups of subjects, by examination of the group × time interaction to evaluate differences resulting from the training programs. Post hoc assessment was undertaken by means of a Bonferroni multiple comparison test. Data are presented as mean ± SD for each group (MST, RT, CG) or percent increase. For all statistical analyses, a p value of 0.05 was accepted as the level of statistical significance.
The data followed a normal distribution. The Kolmogorov-Smirnov test score was 0.09. Before the training period, the subjects did not differ in terms of any variable measured (p > 0.05). After the 6-week program, there were no significant changes in body mass, fat-free mass (FFM), fat mass, percent body fat, or RMR for all the groups (Table 2).
The MST group showed a significant 17% increase (p < 0.05) in 1RM after training. In fact, premean and postmean values were 257.0 ± 58.1 and 299.5 ± 64.3 kg, respectively, whereas no significant differences (p > 0.05) were observed in the RT group and in the CG (Table 3). The MST group showed no significant differences (p > 0.05) in the CMJ, SJ, or STIF tests with the 6-week training protocol. The RT group showed a significant 13% increase in the STIF test (pre: 15.1 ± 3.5 cm vs. post: 17.4 ± 3.7 cm, p < 0.05) and no difference in CMJ or SJ (p > 0.05). The CG showed a significant 7% improvement in CMJ (pre: 26.6 ± 3.0 cm vs. post 28.6 ± 3.7 cm, p < 0.05) and a significant 13% improvement in the SJ (pre 24.0 ± 3.4 cm vs. post 27.2 ± 4.3 cm, p < 0.01) with no difference observed for STIF. All data regarding the 1RM and the jumping ability tests are given in Table 3.
The RE improved significantly (p < 0.05) in the MST group (6.17%) only at marathon pace (second step, Figure 2). No significant differences were observed in the RE for the MST groups at the other running speeds. The RT and CG did not show significant improvements in the RE for any of the running speeds (p > 0.05; Figure 2). The RPE showed no difference from pretraining values at all exercise intensities (p > 0.05).
Studies regarding master athletes have been mainly conducted to understand the rate of performance decline with aging (10,22,43) more than the impact of different training interventions on the physiological variables implicated in endurance performance. Therefore, the main focus of this study was to investigate the impact of a concurrent strength and endurance training on RE in master athletes and understand if the results are similar to those found in young or elite subjects. Accordingly, the results of this study demonstrated a 6.17% improvement in the RE in the MST group, a significant 17% increase in 1RM, with no concomitant changes in body mass, FFM, percent body weight, fat mass, and RMR.
The 17% increase in 1RM observed in this study is lower than what was found in previous studies that evaluated the effects of RT on older adults (19,30). Strength development has been shown to be lower when endurance training is added to a strength training program (19) because the physiological stimuli directed to skeletal muscle as a result of strength training and endurance training are divergent in nature (16). In adding endurance training to strength, a limitation in muscle hypertrophy has been suggested as a mechanism for decreasing gains in strength (31) compared with strength training alone, possibly because of a limited increase in type I fiber area (25). To be effective, especially on endurance athletes, the program needs to maximize increases in 1RM primarily from coordination and neural adaptations and changes in recruitment patterns, with minimal muscle hypertrophy. Less interference is in fact evident when training simultaneously maximal aerobic power and maximal strength because the training stimulus for increasing strength would be mainly directed at the neural system, while the adaptations for increasing maximal aerobic power will mainly induce peripheral adaptations and the interference seems to be less pronounced (7). Moreover, a cross-sectional study on master endurance athletes aged 40–88 years, demonstrated that a significant age-associated decline in leg strength and muscle fiber area and type distribution does not appear until after the age of 70 (44); therefore, chronic endurance training can delay the age of significant decline in peak torque and changes in muscle morphology of the vastus lateralis. This could explain the lower increase in 1RM observed in our study compared with completely untrained older individuals performing an RT program.
Only 1 study evaluated the effects of a strength training program on recreational runners of the same age as our runners (9) but with a lower weekly training volume compared with the runners of this study. The authors found that inserting 2 times a week an MST program in recreational runners had no effect on body weight or composition and no effect on the RE. However, they found an increase in muscular strength that most probably may be advantageous for the endurance runner in a long-term perspective.
More recently, Louis et al. (29) evaluated the effects of concurrent strength and endurance training in master endurance cyclists. Their results indicated age-related differences in cycling efficiency, maximal and endurance torque–generating capacities. In master athletes, the MST program showed an enhancement in maximal and endurance torque production and a reduced age-related difference in performance. In fact, before the strength training, younger individuals showed higher muscular strength and cycling efficiency, whereas after training, the age-related differences were reduced, strengthening the hypothesis that adding a 2 times per week MST to an endurance training program may help reduce the age-related decrements in performance. Therefore, although older individuals have a larger percentage of type I muscle fibers and are therefore able to generate less force (23), they seem to respond positively to RT programs (for a review see ) also when concurrent to endurance training.
Although strength gains in our study are slightly lower, the increase in RE (6% increase found only in the MST) is similar to what was observed for younger individuals. In fact, with an increase in strength, a lower percentage of 1RM in the lower limb extensors will be taxed in each stride, lowering the actual demands of number of motor units recruited (18). Johnston et al. (21) was one of the first groups to associate the effects of the inclusion of a whole-body RT program on the RE in female distance runners. The protocol consisted of a 10-week regimen based on 2–3 sets of 6–20 RM (each set performed to momentary concentric failure) that resulted in significant increases in upper and lower body strength with no changes in body composition and a 4% increase in RE. Similarly, Millet et al. (33) found that the addition of 14 weeks of heavy weight training to the regular endurance program of elite triathletes determined a significant increase in the RE with a 25% increase in lower limb force. Moreover, the MST group showed a significant increase in the velocity associated with V[Combining Dot Above]O2max. Storen et al. (40) showed a 33% increase in 1RM and a 5% increase in the RE in well-trained runners after an additional 2 times a week MST program for 8 weeks. Guglielmo et al. (14) added a 4-week MST and explosive strength training program in well-trained endurance runners. The authors found a 38% increase in 1RM in the MST and a 51% increase in 1RM in the explosive strength training groups, whereas the RE improved only in the MST group. Similarly to Taipale et al. (42), we found an increase in the 1RM only in the MST groups and no change in the RT and in the CG.
Because of the length of the program and because FFM did not change, we can hypothesize that strength gains result from a better motor unit recruitment pattern as previously shown (9). The RMR is largely related to the amount of FFM, and strength training programs focused on hypertrophy have been successfully used in dieting individuals to preserve both RMR and FFM (12). In this study, no significant changes were observed in the RMR and anthropometric parameters, confirming that the strength gains observed are related to neural adaptations rather than to hypertrophy (41). It can therefore be hypothesized that most of the adaptations in the RE may occur already after 4–6 weeks of strength training (as presented in this study) and that longer protocols may not add further improvements in the RE because they might impair further strength gains (31) and expose individuals to nonfunctional overreaching. Moreover, RE improvements of >2.4% can be attributed to the training intervention and not to a day-to-day variability (37).
Strength training has been reported to improve muscle-tendon stiffness (26), and this could be an advantage for improving the rate of force development (47). Kubo et al. (26) was the first group to show the effects of strength training on the elastic profiles of human tendon structures in vivo without noticing a significant hypertrophy. However, we found no difference in STIF in the MST group, whereas the CG and RT groups improved significantly. Animal models show that chronic exercise (endurance training) can modify the elastic proprieties of the tendon (48). This can explain the improvements observed in the CG and RT groups. Similarly to what we found, Millet et al. (33) observed no difference in hopping stiffness and ground contact time in the MST group after 14 weeks of heavy weight training. In accordance with their conclusions, it can be hypothesized that the characteristics of the strength training performed is not optimal for showing improvements in stiffness with a hopping test.
The improvement in CMJ and SJ only in the CG denotes that improvements in 1RM are not sufficient to elicit improvements in jump performance (14). Similarly, Guglielmo et al. (14) found that jump performance increased only in the explosive strength training group but not in the heavy weight training group. Häkkinen et al. (16) showed that individuals who preformed strength training alone showed increases in rapid force production of the trained leg extensors and a significant improvement in rapid neural activation, whereas the concurrent strength and endurance training groups showed no significant changes. These results suggest that concurrent strength and endurance training lead to interferences in explosive strength development as seen also in our study. The authors hypothesize that there may be a reduced improvement in rapid voluntary neural activation (16).
Despite the evidence of significant effects of MST on RE, endurance athletes and in particular Master athletes either include very little or no RT in their regular programs in particular when training volume increases (42). Most individuals still are reluctant and think that adding strength training may impair their progression in endurance performance. Moreover, one of the major concerns in adding strength to endurance training especially in a population that needs to train between already busy schedules is the possible decrease in compliance to training and the risk of nonfunctional overreaching. However, a shorter program (such as ours) seems to interfere less with the decrease in strength gains and avoids the risks of nonfunctional overreaching that are mainly caused when volume of training is extremely elevated and monotonous (32).
Master athletes are a great example of successful aging. They train regularly and in some cases are able to increase performance achieved at younger ages. Most of these athletes are serious and motivated, despite the increasing age, and are willing to perform intensive training sessions for several months to prepare themselves for 1 specific event (45). However, what is till questionable is if they will benefit from the same training programs normally reserved for younger or elite athletes. The results of this study indicate that a well-structured MST program for a limited amount of time during the conditioning training period in preparation of long endurance events can increase the RE, without inducing hypertrophy. What is most interesting is that the RE improvements are similar to what was seen for younger individuals. Because this population has to squeeze training into very busy schedules and optimal training in older adults is fundamentally similar to optimal training in younger athletes, particular attention needs to be paid to the total volume of training during the period of concurrent training to avoid nonfunctional overreaching.
We suggest in the preparation period for major competitions to add a 6-week MST protocol 2 times·per week concurrently to the regular endurance training targeted to increase maximal aerobic power. This could be a beneficial methodology to improve performance in endurance events and a good way to diversify the training program of master runners that often focus only on running, risking nonfunctional overreaching. Because of the restricted age range of this study, these data cannot be generalized to all age categories that include master athletes. Moreover, a wider sample of athletes is needed to evaluate gender differences in the response to an MST protocol.
The authors would like to thank all the participants of the “Villa Ada Green Runners” for the extra time they dedicated to this study. No grant support was provided for this study. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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