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Original Research

Changes in Physical Size Among Major League Baseball Players and Its Attribution to Elite Offensive Performance

Crotin, Ryan L.1; Forsythe, Charles M.2; Bhan, Shivam3; Karakolis, Thomas3

Author Information
Journal of Strength and Conditioning Research: October 2014 - Volume 28 - Issue 10 - p 2705-2708
doi: 10.1519/JSC.0000000000000475
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Understanding the relationship between physical size and superior athletic performance has long been a focus for clinicians, sports scientists, collegiate recruiters, and professional scouts (1,3,10,11,22,25), with interest dating back to the end of the 19th century (2). Talent evaluators and researchers alike have attempted to determine the fundamental physical and physiological attributes that are most important for success in each sport, event, and position. However, as the anthropometrics of the general population have changed remarkably over time (5,7–9,13,17,24), so have the physical characteristics of the elite athlete population (14,16,18–20,26,27). Previous work by Norton and Olds (16) charted height, mass, and body mass index (BMI) changes for athletes in various sports over the 20th century. However, their work did not cover professional baseball, and in particular Major League Baseball (MLB) players.

Major League Baseball is one of the world's oldest professional spectator sports and has a storied and extensive tradition of classifying statistical and physical metrics of its athletes. Strength and conditioning programs have slowly evolved since the early 1980s to become an institution within MLB, which further investigated anthropometric associations to statistical prowess and competitive development (6,12,15). Class A players, competing in the lowest level of professional competition, typically weigh the least and represent the leanest subgroup, demonstrating body mass and percent body fat gains to a maximum upon reaching the major leagues (12). Aging appears to be a prominent influence on physical growth, as players 29–31 years old were found heaviest with the highest body fat percentages within a 20- to 35-year age range (15).

At the inception of strength and conditioning in professional baseball, portable instruments to assess body fat percentages were absent and as a result, player anthropometrics owed to height and body weight measurements. Therefore, to compare body mass proportions longitudinally, calculation of players' BMIs would be sufficed. As an extension to the work of Norton and Olds (16), this study aims to discover if MLB experienced similar growth trajectories as seen in other sports, hallmarked by increased physical size throughout baseball's modern era (1970–2010), where competitive seasons were expanded to 162 games and included the American League's designated hitter. Therefore, the purpose of this study was to identify height, weight, and BMI changes in the normal MLB population (MLB), as well as in offensive league leaders (OLL) over 3 separate seasons within the modern baseball era (1970, 1990, and 2010). Anthropometric differences seen between elite offensive performers and the MLB reference cohort will also be explored to identify a possible connection between physical size and elite offensive performance, where strength and conditioning coaches can be integral to furthering physical development in professional baseball. We anticipate that major league players have increased in physical size (height, weight, and BMI) successively from 1970, 1990, and 2010. Second, we anticipate that physical size will have an association to elite performance, as league leaders are expected to be larger than their reference cohorts.


Experimental Approach to the Problem

Players' heights and weights are recorded at the time when the professional contract is signed. The 20-year gap between seasons was selected to represent competitive conditions during 3 distinct epochs, and to minimize overlap of players for anthropometric analyses between cohorts meaning players had less than 20 years of Major League service in the current study. An OLL group was created, consisting of all players in the top 10 of at least 1 of the following statistical categories: total homeruns, slugging percentage, batting average, on-base percentage, runs scored, runs batted in, and on-base plus slugging percentages. Offensive league leaders were not included in the reference population (MLB group), allowing for within- and between-subject height, weight, and BMI comparisons.


In total, 1,896 MLB offensive players were analyzed (age, 28.0 ± 4.07 years; height, 1.85 ± 0.53 m; mass, 88.2 ± 9.84 kg; BMI, 25.8 ± 2.34 kg·m−2) from 3 separate seasons (1970, 1990, and 2010). No human subjects were involved in the study, where all performance statistics, age, body weights, and heights were obtained from, a publicly available, online provider carrying licensed MLB Data (


Body mass index calculations were performed on all subjects by dividing the player's kilogram mass by the squared height in meters (BMI = mass (kg)/height2 (m)).

Statistical Analyses

A mixed design analysis of variance examined anthropometric differences, with the time (year epoch) influence on individual anthropometric characteristics (height, weight, BMI) as the repeated-measures factor, where a Bonferroni correction factor was applied for post hoc testing. Independent t-tests compared anthropometric characteristics between OLL and MLB reference cohorts of the same year. All statistical analyses were performed using an α of 0.05.


Table 1 presents within- and between-group differences for MLB and OLL mean heights, weights, and BMIs over the 3 seasons studied. Repeated-measures tests showed successive increases in body mass (1.2% increase from 1970 to 1990; 11.7% increase from 1990 to 2010) within the MLB cohort impacting BMI values most from 1990 to 2010 (p < 0.001), whereas height significantly increased by 0.54% from 1970 (p ≤ 0.05) followed by a stabilizing period after 1990. Within OLL, height decreased by 0.53% between 1970 and 1990 (p ≤ 0.05), whereas BMI successively increased from 1970 onward (p ≤ 0.05). As seen in the MLB reference population, statistical leaders presented greatest mass and BMI gains from 1990 to 2010 (p < 0.001), increasing by 11.8% and 9.1%, respectively.

Table 1:
Anthropometric comparisons within and between cohorts at 1970, 1990, and 2010.*

Compared with the reference population, 1970 offense leaders were 5 cm taller (OLL 1.87 ± 0.06 m vs. MLB 1.83 ± 0.5 m, p < 0.001), more than 5 kg heavier (OLL 88.5 ± 10.0 kg vs. MLB 82.9 ± 6.81 kg, p < 0.001), which elicited greater BMI values (OLL 25.4 ± 2.05 kg·m−2 vs. MLB 24.6 ± 1.54 kg·m−2, p = 0.001). In 1990, OLL remained taller by 2 cm (OLL 1.86 ± 0.06 m vs. MLB 1.84 ± 0.5 m, p = 0.013) and were approximately 8 kg heavier (OLL 91.6 ± 11.1 kg vs. MLB 83.9 ± 7.51 kg, p < 0.001), giving rise to a higher BMI (OLL 25.4 ± 2.05 kg·m−2 vs. MLB 24.6 ± 1.54 kg·m−2, p < 0.001). In the most recent decade, 2010 OLL were 4 cm taller (OLL 1.89 ± 0.05 m vs. MLB 1.85 ± 0.5 m, p < 0.001), 8 kg heavier (OLL 102.4 ± 8.26 kg vs. MLB 93.7 ± 8.73 kg, p < 0.001), showing the greatest anthropometrics and overall BMI over the 40-year analysis (OLL 28.8 ± 2.04 kg·m−2 vs. MLB 27.4 ± 2.10 kg·m−2, p < 0.001).


Baseball research on anthropometrics investigated associations to position (4), age (15), and professional development (12) but lacks longitudinal tracking in how players' bodies evolved to present. Our anthropometric examination identified longitudinal trends, evidencing increased physical size among players of the modern era. Overall, nearly 10 kg (22 lbs) of body mass was gained from 1990 to 2010, representing approximately a 12% increase. Whereas height displayed smaller growth patterns showing no more than 3 cm growth, representing less than 2% increase. An unanticipated decrease in height was shown for OLL from 1970 to 1990, being the only significant reduction in body size; yet, OLL were found taller, heavier, with greater mass proportionality over successive years when compared with the MLB reference cohort.

Since OLL were found physically larger, size may be associated with greater offensive performance, which supports previous work. Carvajal et al. (4) studied physical size in relation to playing position and performance among Cuban professional baseball players over 2 competitive seasons, where first basemen, representing largest body mass, were found to be statistically best. Hoffman et al. (12) analyzed player development in baseball, discovering a moderate correlation between greater lean body mass and higher homerun totals, slugging percentages, and total bases. Hoffman et al. (12) also found that with greater body mass, grip strength dynamometry and lower-body power were improved, which likely contributed more to statistical performance than anthropometric characteristics alone.

The work of Saint Onge et al. (21) is the longest anthropometric examination in the literature, documenting professional baseball players' heights, weights, and BMI over a 115-year period from 1869 to 1983 to represent growth patterns within the general U.S. population. Major League Baseball players born in proximity to 1983 gained 7.6 cm in height and 12.2 kg of weight from those born in 1869, reflecting improved nutrition, training, and sanitation. U.S. players born within 1979–1983 achieved a mean body weight of 195.7 lbs (21), whereas our 2010 findings showed players approximately 10 pounds heavier, weighing over 206 lbs, which documents the largest professional baseball population to date (4,12,15,21). In contrast, lesser height gains shown in the present is perhaps associated to the influx of Latin players from 1990 onward, which were shown to be shorter than players of non-Latin descent (21).

Players' heights and weights are indexed on the day they are professionally signed; therefore, our results may reflect an increased interest in selecting players of greater physical size over the last decade. Scouting criteria during the modern era further qualifies baseball attributes by somatotype, expressing players' body shapes and growth potential throughout maturity (23). Typically, physical profiles are communicated by scouts through referencing an athlete's body type to existing MLB players (4,23). The transition in recruiting larger prospects is speculated to be a result of better performances shown by larger players over time; yet, increased anthropometrics in the general U.S. population may also have contributed to this observation (21). Therefore, we cannot fully determine if both size and skill advanced in parallel, but we can conclude that professional baseball players with greater BMI appear to perform better offensively.

Our study was limited by the absence of body composition data, as current and retrospective records are unavailable for public access and precludes documenting longitudinal changes in muscle and fat mass proportions. Better nutrition, sanitation, and training methods reportedly increased players' physical size from 1869 to 1983 (21); yet, these aspects were well established during the last decades examined in our study and had less influence in advancing players' physical size. By the early 1990s, strength and conditioning coordinators administering weight training programs became more mainstream in professional and collegiate baseball (6), which may have enticed anabolic drug use to surface outside organizational policy. It is possible that both entities contributed to mass gains seen in 1990 and a decade later in 2010. By 2010, MLB players were found largest, which likely owed to multifactorial causes, as a combination of exposure to strength and conditioning programs at early age, throughout high school and collegiate baseball, better sports nutrition, and anabolic drug use might be responsible for drafting larger players. Comparatively, 1970 MLB records presented significantly lower-body mass proportions for which the aforementioned factors were not as widely popularized in baseball.

Practical Applications

Body mass index calculation provided a suitable method to evidence growth trends among MLB players and can be assessed at any historical point in time. Although our results suggest that increased mass relative to height is an attribute of elite offensive performance in mechanically proficient athletes, continual growth may not be orthopedically advantageous and may hamper running speed, lower- and upper-body power, joint mobility, cardiovascular responsiveness, and resistance to injury. Likewise, a reduction in mass relative to height may present the same undesired consequences, and certainly, access to body composition records would further delineate how changes in height, fat, and fat-free mass influence performance, where MLB teams monitoring player anthropometrics can identify individual optimums. The role of the strength and conditioning coach in baseball is vital in regulating fat and fat-free mass proportions, where it may be desired to integrate additional hypertrophy phases for players revealing lean body mass losses, and greater caloric expenditures for those gaining body fat. Fear of injury in some instances can lead team administrators, coaches, and medical staff to stifle strength and conditioning approaches that involve greater training loads, such as complex lifts (squat, deadlift, bench press etc.), where the current study infers administering such training methods under qualified supervision to add value to respective athletes in making physical gains. In signing a professional contract, it appears that larger players are more coveted by scouting departments, where earlier participation in structured, drug-free nutritional and strength and conditioning programs can provide athletes greater opportunity for success in MLB.


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anthropometrics; height; weight; BMI; batting; hitting; baseball

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