Elite athletes often undergo performance testing, and although there may be volumes of data on these athletes, it is rarely published or available for review. Despite this particular scarcity, many studies have investigated aerobic fitness over time. Most studies have measured the decline in aerobic fitness with aging using participants with average or variable degrees of fitness (2,14,25,33). The early work by Robinson (32) and Åstrand (1,2) set the stage for longitudinal studies conducted by Dill et al. (15) and, later, by Robinson et al. (34). Trappe et al. (39) provided additional information regarding aging among athletes. However, most of the data on aerobic fitness from the last several decades have been cross-sectional rather than longitudinal, and studies often include older adults who have not maintained a high level of fitness over time.
Therefore, the purpose of the present study was to evaluate a group of elite male distance runners, who were the best in the United States in the late 1960s and early 1970s, as long as possible (45 yr). By collecting these longitudinal data, we hoped to provide a unique description of changes in cardiorespiratory fitness of aging elite athletes who continued to be physically active. Specifically, the aim of this study was to measure the changes in cardiorespiratory capacity and running economy of these athletes during aging. This is important not only from a physiological standpoint but also because maintaining adequate fitness in later years is important for retaining functional independence (36). Thus, results from this study may provide additional perspectives on benchmarks for fitness with aging.
Twenty-six elite male distance runners, ranked in the top 10 in their best running event, were recruited for the present study. All 26 competed in the United States 1968 Olympic Trials. The present study was approved by the local institutional review board, and all athletes gave their written informed consent to participate.
Participants were tested the week before the 1968 Olympic Trials (11) and again in 1993 and 2013. During each testing session, age, mass, HR, V˙O2max, ventilation, and running economy were assessed. There was a doctor present during the testing sessions in 1993 and 2013. In 1968 and 1993, exercise HR values were measured by palpation under the left pectoral muscle; in 2013, a Polar HR monitor (Lake Success, NY) was used. HR was measured in beats per minute. Predicted HRmax was also calculated for each session using the formula: 220 − age, and the more recently developed formula 213.2 − 0.78 × age (30).
To assess cardiorespiratory capacity, V˙O2max and maximal minute ventilation (V˙Emax) were used. Participants completed a V˙O2max test on the treadmill or cycle ergometer to assess aerobic fitness. V˙O2max is expressed in milliliters per minute per kilogram. For data from 1968 and 1993, V˙O2max was normalized to the current weight and to the original weight of participants as measured in 1968 to evaluate the effect of weight change on V˙O2max. For respiratory and metabolic measures in 1968 and 1993, expired air samples were collected in meteorological balloons and analyzed for CO2 and O2 fractions using a Lloyd–Gallenkamp chemical analyzer; in 2013, Parvo Medics TrueOne 2400 metabolic measurement system (Salt Lake City, UT) was used for analyzing and recording these data (8,12). The average values for the highest four consecutive 15-s V˙O2 values presented were used to describe V˙O2max and all corresponding HR, V˙Emax, and ratio of V˙Emax to V˙O2max data. The ratio of V˙Emax to V˙O2max was calculated for each session.
To calculate running economy (mL·kg−1·km−1), participants performed a self-selected submaximal run at a pace that the athletes believed they could maintain for 30 min. Running economy was calculated for only the 12 participants who performed running V˙O2max tests at each testing session. Running economy is often expressed in milliliters of oxygen consumed, per minute, per kilogram bodyweight, but in this study running economy was expressed in milliliters of oxygen, per unit distance (km), per kilogram body weight to normalize for individuals running at different speeds. When runners are not running at the same speed, or at the same relative V˙O2max for the tests, the logical comparison is then to use distance covered (mL·km−1·kg−1) instead of pace. For example, if a runner tested at a speed of 268 m·min−1 has a V˙O2 of 50 mL·min−1·kg−1, this means it will take 3.73 min to run 1 km (1000/268). This runner’s economy will then be 3.73 × 50 = 187 mL·km−1·kg−1. Another runner, or the same runner when not in an equal state of fitness, who can only run at an economy test speed of 200 m·min−1 and consumes 40 mL·min−1·kg−1 will have an economy value of 200 mL·km−1·kg−1 (40 × 5 min to complete 1 km). The higher the economy number, the poorer the economy factor.
Outcomes from all participants were summarized as mean ± SD. For the 10 participants who performed the V˙O2max test on the cycle ergometer in 2013, the mean group results were calculated with and without a 7% correction factor for the cycle ergometer V˙O2max tests (13,18,28,31). The results did not differ with and without the correction factor, so data from all 22 participants were combined in the final analysis. Data were analyzed with SPSS statistical software, version 23 (IBM Corp., Armonk, NY), using generalized linear models to compare differences in variables by year. Post hoc analyses were performed using a sequential Bonferroni correction for multiple comparisons. Finally, the V˙O2max of the participants in the present study (longitudinal data) was compared to the American College of Sports Medicine average percentile values (38) for males (cross-sectional data) in the 99th and 50th percentiles (as two benchmarks for aerobic fitness) for each of the age ranges pertaining to the data collection testing sessions of the present study. Significance level was set at P < 0.05, two-tailed.
The 26 elite male distance runners who participated in the present study in 1968 were World Record holders, National Champions, and Olympic gold, silver, and bronze medalists. Fifteen of the 26 had qualified for competition in one or more Olympic Games. The mean ± SD age of participants in 1968 was 24 ± 2.8 yr, and the mean ± SD mass was 67 ± 5.7 kg. In 1993, the same 26 athletes completed testing, and mean age and mean mass were 49 ± 2.8 yr and 75 ± 9.2 kg, respectively. In 2013, 22 athletes completed the testing: three passed away between 1993 and 2013 and one declined to participate in 2013. The mean age of participants in 2013 was 69 ± 2.8 yr, and the mean mass was 77 ± 12.8 kg. The mean mass was greater in 1993 and 2013 than that in 1968 (both P < 0.001).
The mean ± SD HRmax values were 178 ± 10.6 bpm in 1968, 176 ± 13.1 bpm in 1993, and 168 ± 16.4 bpm in 2013 (Fig. 1). The mean 220 − age predicted HRmax values were 197 ± 2.6 bpm in 1968, 172 ± 2.6 in 1993, and 151 ± 2.9 in 2013. The mean predicted HRmax values using the formula developed by Nikolaidis (30) were 195 ± 2.2 bpm in 1968, 177 ± 2.2 in 1993, and 160 ± 2.2 in 2013. The measured HRmax was different from the HRmax predicted by both formulas in 1968 and 2013 (both P < 0.001).
The mean ± SD V˙O2max values for participants were 78 ± 3.1 mL·min−1·kg−1 in 1968, 57 ± 6.7 mL·min−1·kg−1 in 1993, and 42 ± 8.9 mL·min−1·kg−1 in 2013 (Fig. 2). V˙O2max values in 1993 and 2013 based on the original 1968 body weight were 65 ± 6.0 and 47 ± 8.1 mL·min−1·kg−1, respectively, and were higher than the actual V˙O2max for those years (both P < 0.001).
The mean ± SD V˙Emax values were 177 ± 13.1 L·min−1 in 1968, 150 ± 24.9 L·min−1 in 1993, and 118 ± 22.5 L·min−1 in 2013. V˙Emax significantly declined at each time (both P < 0.001) (Fig. 3).
The ratio of V˙Emax to V˙O2max was 34 in 1968, 35 in 1993, and 38 in 2013. The ratio was greater in 2013 than that in 1968 (P < 0.003) (Fig. 4). V˙Emax measured in 1968 was highly predictive of V˙Emax measured in 2013 (R2 = 0.57, P < 0.001). V˙O2max measured in 1968 was not predictive of V˙O2max measured in 2013 (R2 = 0.11, P = 0.133). However, the change in V˙O2max between 1968 and 2013 was strongly associated with change in V˙Emax between 1968 and 2013 (R2 = 0.63, P < 0.001).
The mean ± SD running economy values were 196 ± 7.0 mL·kg−1·km−1 in 1968, 205 ± 16.5 mL·kg−1·km−1 in 1993, and 240 ± 27.0 mL·kg−1·km−1 in 2013. Running economy was significantly greater in 2013 than that in 1968 and 1993 (both P ≤ 0.001) (Fig. 5).
When comparing the V˙O2max of participants in the present study with American College of Sports Medicine average percentile values (38), participants of the present study were above the 99th percentile value for V˙O2max for their age-group in 1968 (Fig. 6). In 2013, participants were slightly below the 95th percentile.
To our knowledge, this study provides the longest report of changes in cardiorespiratory fitness and running economy with aging in Olympic-caliber running athletes. In 1968, 26 elite male American distance runners were tested for aerobic fitness (11), and those data became the first testing session of the present study. In total, data were collected on these individuals three times for 45 yr, providing a unique, longitudinal picture of changes in cardiorespiratory fitness with aging. Our participants were elite athletes in their 20s but not in their 60s. However, they had maintained an aerobic fitness level that was near the 95th percentile for population norms (38). This finding contradicts the accepted notion that a decline in aerobic fitness with age is obligatory (4,17). The four most active individuals (as characterized by self-reported weekly activity in 2013) exercised between 300 to 600 min·wk−1 (depending on the individual), and all had a V˙O2max of 45–50 mL·min−1·kg−1 (with all being >66 yr old). By comparison, another participant reported exercising only 60 min·wk−1 and had a V˙O2max of 32 mL·min−1·kg−1. This speaks to the fact that habitual activity can blunt the decrease in V˙O2 with aging (20). Such examples also reinforce the challenges of using cross-sectional data when developing individualized expectations for fitness, especially among adults who have a wide range of activity levels.
Skeletal muscle strength, endurance, and cardiorespiratory fitness are known to decline in older adults. However, there are conflicting reports about whether this reduction in skeletal muscle function is due to inherent defects, such as mitochondrial dysfunction (6,29), or due to changes in lifestyle and activity patterns. In a review by Evans (16), evidence suggested that age-associated decline in muscle strength and oxidative capacity can be reversed or prevented with appropriate nutrition and exercise strategies. Studies looking at cardiovascular fitness changes across a person’s life span are more difficult to perform because of the logistical difficulties of longitudinal studies and the rarity of finding participants willing and able to engage in consistent, lifelong physical activity. Therefore, the relationship between a decline in fitness due to a lack of activity (17,37) and the effects of aging alone (i.e., time) has not been widely studied. To our knowledge, this study was the first to collect longitudinal data on elite endurance athletes older than 45 yr. Our results demonstrated that these participants maintained a relatively high level of age-related cardiorespiratory fitness for 45 yr, which reinforces the importance of recommendations to maintain continued physical activity throughout life.
The HRmax values measured in the present study were similar to those reported for previous champion athletes (34,39) and for nonathletes of similar age (3,25,35). However, the current participants did not show a drop in HRmax with aging, which contradicted the study by Trappe et al. (39).
The decline of V˙O2max in our study was comparable with similar age-span participants in studies by Åstrand et al. (3), Robinson et al. (33), and Robinson (32), who looked at noncompetitive participants. Our results were also similar to those of Robinson et al. (34), who longitudinally studied champion runners 24–48 yr of age. Nonelite individuals tend to have a smaller rate of decline in V˙O2max associated with each year of aging compared with elite athletes, which is likely because elite athletes would start a longitudinal study in a highly trained state within a small margin of their absolute potential for V˙O2max. If these elite individuals stop training, over time they will lose V˙O2max for two reasons: age and detraining. Research participants who are less fit when they begin a longitudinal study or who provide cross-sectional data do not lose as much V˙O2max due to detraining because they were not highly trained at the beginning of the data collection. Also, the annual loss in V˙O2max is probably not similar for all individuals (20), and tests performed more often would give a clearer picture of the pattern of decline in V˙O2max with aging. Although ongoing exercise is necessary to ward off the effects of aging on aerobic capacity, years of prior exercise do not prevent an age-associated decline in cardiorespiratory fitness. However, reinitiating a training program, after years of sedentary living, can still elicit an improvement in cardiorespiratory fitness, even among older individuals (33,35).
Although the participants in the present study were very fit individuals in their 20s and 40s, they still experienced the typical effects of aging known to occur in the later decades of life (26,27). V˙O2max declined at each testing session in our study. Interestingly, if the participants had maintained their original body weights, the decline in their relative V˙O2max would have been substantially less, and they would have had relatively higher cardiorespiratory fitness in 1993 and 2013. This result underscores the importance of avoiding weight gain later in life, preferably by maintaining an active lifestyle.
Similar to V˙O2max, V˙Emax declined with age. Also, the reduction in V˙Emax significantly predicted the reduction in V˙O2max. Remarkably, the decrease in V˙O2max between 1968 and 2013 was more strongly associated with the change in V˙Emax (R2 = 0.63, P < 0.001) than with the initial fitness level (V˙O2max in 1968) (R2 = 0.11, P = 0.133). One explanation for this could be that the decline in ventilation was driving the decline in V˙O2max. However, we cannot rule out the effects of a lower absolute metabolic demand as a separate contributor to the decline in V˙O2max. Also, the HRmax was unchanged over time. Realizing that other physiological changes occurred in these athletes, the decrease in V˙Emax was a significant predictor of the decrease in V˙O2max. This suggests that ventilation plays a role in the age-associated decline in V˙O2max (19). Despite the drop in V˙O2max in 45 yr, these athletes were still at or above the 95th percentile for their age-group (60–70 yr) in 2013 when compared with the general population (38). However, the slope of the decline of V˙O2max in our participants was greater than the cross-sectional standards of the American College of Sports Medicine.
This result stresses the importance of longitudinal data, as opposed to cross-sectional data, when establishing population norms for fitness. Although our participants were elite athletes as younger adults, the expectations for average fitness with aging may need to be revisited because cross-sectional data from largely sedentary participants may create expectations that are too low (26,27,38). Another possible explanation is that higher initial fitness in young adulthood may be a protective factor with aging, leading to higher overall fitness throughout the life span (20). If additional data support that higher initial fitness in younger years contributes to higher fitness with aging despite an expected aging-related drop in fitness, this explanation would further emphasize the importance of maintaining robust physical activity, including in young adulthood, and of avoiding weight gain later in life.
Therefore, we should encourage younger adults to achieve and maintain a higher level of cardiorespiratory fitness because it may protect them against age-associated decline in function that could lead to a loss of function and independence (24,35,40). Research suggests that a V˙O2max of 15–18 mL·min−1·kg−1 is the minimum fitness required for independent activities of daily living (36). Using that standard, the participants in the present study were 2.5 times above the minimum cardiorespiratory fitness for maintaining functional independence. The expected cardiorespiratory benchmark is important for physical activity recommendations for older adults. Furthermore, research suggests a strong positive correlation between physical activity and overall quality of life for all adults (5) and especially for older adults (37). Thus, recommendations for cardiorespiratory fitness with aging could be improved with more longitudinal data that show a high age-related level of fitness can be maintained over several decades, such as from the present study and others (21–23). Thus, although V˙O2max declines with age, continued training seems to offer more cardiorespiratory margin in later years. However, the rate of decline in active individuals is different from those who are not as active, and this difference is exacerbated in older people (20). This underscores the importance of longitudinal data to accurately represent the rate of change in V˙O2max with aging.
Another outcome of the present study evaluated running economy in these athletes. Running economy was evaluated in each of the three testing sessions using an established method (7,9,10). To our knowledge, data from the present study provide the first account of a longitudinal measurement of running economy. Running economy declined at each testing session (O2 cost increased) and significantly declined between 1993 and 2013. This result suggested a stronger (inverse) relationship between running economy and increasing age and possibly ventilation (19). Additional research is needed to better understand the mechanisms responsible for the decline in running economy with aging.
Some limitations of the present study include the small sample size. However, 85% of the original participants were retained over more than four decades. Another potential limitation is that the methods for testing V˙O2max changed over the decades as more modern equipment became available. In addition, our study population was unique, and the results should be interpreted accordingly for the general population.
Future research should assess lung function and collect muscle biopsies to measure oxygen delivery and muscle oxygen utilization to determine whether the age-associated decline in V˙O2max is being driven by a reduction in respiratory mechanics, lung function, oxygen delivery, or oxygen utilization. The degree to which each of these factors is contributing to the decline in V˙O2max should be investigated. Results from the present study add to the longitudinal picture of aerobic fitness across an individual’s life span and may be an important addition to the literature for benchmarks of fitness during aging.
The authors gratefully acknowledge the dedication of the participants and their willingness to travel from as far as Pennsylvania to Hawaii to perform these rigorous exercise tests. We thank the A.T. Still University Aging Studies Project for supporting some of the travel costs for the participants. We also thank G. Krahenbuhl, M. Hopman, A. Asendorf, and T. Fiel for their help with the data collection for this study. Finally, we thank Deborah Goggin for her comprehensive edits of this manuscript.
The authors have no relationships with companies or manufacturers who may benefit from the results of this study. The results of this study do not constitute endorsement by the American College of Sports Medicine. The authors declare that the results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.
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