Although the biomechanical aspects of baseball pitching have been extensively studied by researchers (9,10), considerably less focus has been placed on the physiological aspects. Baseball pitching is considered to be an extremely high intensity, short-duration task that is repeated by the pitcher numerous times during the course of a game (18), and thus, the task of baseball pitching is generally considered to be a physiologically anaerobic activity (19,22).
However, due to limitations in the ability of researchers to collect physiological data (e.g., oxygen uptake) during in-game baseball pitching, little research examining the in-game physiological intensity associated with baseball pitching has actually been previously conducted. Thus, it is difficult for strength and conditioning practitioners to create training programs that are specific to the physiological demands of the task of baseball pitching. Due to the direct relationship between heart rate (HR) and oxygen uptake (V̇o2) (24), another method of examining the physiological intensity of an activity is to monitor the HR of an individual during that activity (1). Based on this relationship, the expression of an individual's HR as a percent of their maximal HR (%HRmax) is commonly used by practitioners to indirectly monitor the intensity of an activity or exercise (11).
This method of indirectly characterizing the intensity of a task through the use of HR has also been previously used by researchers to examine the intensity level of baseball pitching as well (2,8,17,20,23,26). However, the vast majority of these investigations have examined the HR associated with baseball pitching during simulated games (2,8,17,26) or bullpen sessions (23). Beiser et al. (2) examined the in-game HR response to baseball pitching, but this was during an intrasquad game and, thus, does not necessarily reflect the true competitive nature associated with in-game baseball pitching. As such, to date, the study by Stockholm and Morris (20) is the only investigation of in-game HR during actual competitive baseball pitching. However, these data were only collected during a single baseball game and among a single baseball pitcher. Finally, all of these previous investigations have only examined the in-game HR responses among high school or collegiate-level baseball pitchers, and thus, the in-game HR responses among professional-level baseball pitchers remain uncharacterized.
Furthermore, previous research suggests that a home field advantage exists in athletics (14), which has been hypothesized to be the result of psychological factors such as confidence, motivation, and arousal level (16). In addition, owing to the link between mental stress and HR responses (3,4,25), it is possible that the psychological stressors associated with competitive baseball pitching may influence the in-game HR responses of baseball pitchers. As such, it is possible that the unique differences between pitching at home vs. on the road (away) may influence the HR responses associated with baseball pitching as well.
Therefore, the true in-game HR responses between home and away games, and across innings, have not been adequately characterized during competitive baseball pitching. Consequently, the physiological intensity of competitive baseball pitching among professional-level baseball pitchers remains largely unknown. Accordingly, the primary purpose of the current study was to characterize the in-game HR response of baseball pitching among professional baseball starting pitchers and to compare this HR response across innings. A secondary purpose of the current study was to examine potential differences in the in-game HR observed between home and away starts. It was hypothesized that a higher in-game physiological intensity would be observed among away games when compared with home games. Preliminary results from this investigation have been previously published in abstract form only (5).
Experimental Approach to the Problem
This study characterized the HR responses of baseball pitching during competitive games. This was accomplished by investigating the descriptive statistics of the mean in-game %HRmax data and by examining the potential interaction effect between game location (home vs. away) and inning among professional baseball starting pitchers. As such, the dependent variable of the current study was in-game %HRmax and the independent variables included game location (home and away) and inning (1–6).
Sixteen Single-A male professional baseball starting pitchers volunteered to participate in the current study (mean ± SD at the start of season, age = 22.1 ± 1.3 years; height = 187.9 ± 4.4 cm; weight = 90.5 ± 9.5 kg). This study occurred during the pitchers' actual competitive season, and all data were collected during live competitive games. All participants were at least 18 years of age (range = 19–24 yrs) and were healthy and free from any musculoskeletal injury that prevented them from pitching during a normally scheduled start, as determined by the baseball club. The protocols utilized in this study were approved by the institutional review board (IRB) of the University of Wisconsin-Milwaukee and all participants provided written informed consent before any data were collected.
In-game HR data [(beats per minute (bpm)] were collected using Bioharness 3 wireless physiological status monitors (Zephyr Technology Corp., Annapolis, MD) at a sampling rate of 250 Hz. These in-game HR data were collected until either the pitcher was removed from the game or when 6 innings of pitching were completed. Due to uncontrollable events (e.g., injury, transfer to different team, trades, etc.) and individual variance in pitching performance (e.g., being removed before reaching 6 innings pitched), it was not possible to collect the same number of innings pitched across all participants. As such, the number of innings pitched across participants ranged from 8 to 104 (Table 1) and the total number of innings collected for each respective inning (1–6) ranged from 31 to 153 (Table 2).
Only in-game HR data collected after each pitcher completed their respective warm-up pitches and before each pitcher returned to the dugout at the conclusion of an inning were analyzed. These time points were identified in the data sets through timestamps representing the beginning and the end of each inning for each game, which were provided by the baseball team staff. These in-game HR data were then averaged for each inning of each game for each individual pitcher. To collapse the in-game HR data across participants, all in-game data were then normalized to each pitcher's age-predicted maximal HR (220–age) to create a %HRmax for each individual pitcher for each inning across the entire baseball season.
Descriptive statistics (mean ± SD) among all participants (Table 1) were calculated. In addition, a split-plot mixed-model repeated-measures analysis of variance (RM ANOVA) was used to examine the interaction effect of inning × game location, as well as the simple effects of inning (1–6) and game location (home and away) on in-game %HRmax. All statistical analyses were conducted using IBM SPSS 22 statistical software (IBM Corp., Armonk, NY), and an alpha of 0.05 determined statistical significance for all analyses. Effect sizes were evaluated using a η2p (partial eta squared), with η2p < 0.06, 0.06 ≤ η2p < 0.14, and 0.14 ≤ η2p indicating a small, medium, and large effect, respectively (13).
Post hoc visual inspection of the distribution histograms and Q-Q plots, indicated 2 outliers in the %HRmax data. As such, these data points were removed, resulting in a total of 682 innings (home = 381; away = 301) included in the statistical analyses. After the removal of these outliers, Levene's tests of homogeneity of variances indicated equal variances across innings (F5,676 = 0.551, p = 0.738), as well between home and away starts (F1,680 = 2.916, p = 0.088), among the %HRmax data. As such, a normal distribution and equal variances were observed across all analyzed %HRmax data.
The group mean ± SD in-game %HRmax across all innings was 84.8 ± 3.9% (Table 1). The results of the split-plot mixed-model RM ANOVA identified a statistically significant interaction effect between inning × game location (F5,520 = 2.375, p = 0.042, η2p = 0.079). Follow-up simple effects of inning indicated that the in-game %HRmax was significantly different across innings, but only during home starts (F5,294 = 10.245, p < 0.001, η2p = 0.202) and not during away starts (F5,226 = 1.300, p = 0.268, η2p = 0.048). Specifically, follow-up pairwise analyses indicated that the in-game %HRmax during home starts in the first and second innings were significantly (p ≤ 0.05) higher than all other innings, with the in-game %HRmax also being significantly (p ≤ 0.05) higher in the first inning than in the second inning (87.3 ± 3.6% vs. 85.0 ± 3.4%, respectively). However, no significant (p > 0.05) differences were identified among the in-game %HRmax data between any other innings (third through sixth). These results suggested that the mean physiological intensity of pitching changes during the course of the game, as the %HRmax data were significantly higher in the first 2 innings, but that this change is only apparent during home starts and not during away starts (Table 2).
Furthermore, follow-up simple effects of game location indicated that the in-game %HRmax was significantly (F1,151 = 5.866, p = 0.017, η2p = 0.037) different between home starts and away starts in the first inning (Figure 1). All tests of simple effects of game location among innings 2–6 were not statistically significant (p > 0.05). This implies that the mean in-game pitching intensity was significantly higher during home starts than away starts, but only in the first inning (87.3 ± 3.6% vs. 85.8 ± 3.8%, respectively).
The primary purpose of the current study was to characterize the in-game HR response of baseball pitching among professional baseball starting pitchers and to compare this HR response across innings. The mean age-predicted in-game %HRmax value of 84.8% among all participants suggests that baseball pitching is an extremely high-intensity task. As such, the physiological intensity associated with baseball pitching among professional starting baseball pitchers does seem to be primarily anaerobic in nature, which is in agreement with many of the long-held beliefs among practitioners regarding the physiological intensity of pitching (19,22).
However, this mean in-game %HRmax value of 84.8% in the current study is also considerably higher than many of the HRs observed during baseball pitching in other previous studies. For example, Crotin et al. (8) observed a mean in-game HR of 124.6 bpm, Warren et al. (26) observed a mean in-game HR of 133.5 bpm, Potteiger et al. (17) observed a mean in-game HR of 140 bpm, and Szymanski and Meyers (23) observed a mean in-game HR of 151.2 bpm. Based on the mean ages of the participants provided by the researchers of these respective studies, these in-game HRs are equivalent to age-predicted %HRmax values of 62, 67, 70, and 75%, respectively. However, these previous studies have all examined HRs associated with baseball pitching during simulated games (8,17,26) or bullpen sessions (23). Thus, based on the results of the current study, the simulated games or bullpen sessions examined by previous researchers may underestimate the actual in-game physiological intensity associated with baseball pitching among starting baseball pitchers.
Conversely, when examining the HRs associated with baseball pitching during intrasquad games, Beiser et al. (2) reported an in-game HR range of 164–179 bpm (no mean in-game HR was provided), which based on the mean age of the participants, is equivalent to an in-game %HRmax range of 82–90%. The observed %HRmax range observed by these researchers is similar to the mean in-game %HRmax observed in the current study (84.8%), although the current study had a larger overall range (72.4–95.9%). This larger range in %HRmax values may potentially be due to the fact that the current study collected data from a larger sample population (16 vs. 7) and a much larger number of total innings (682 vs. unknown). However, the data from the current study and from Beiser et al. (2) suggest that the in-game physiological intensity of baseball pitching is higher than the reported intensity during simulated games and bullpen sessions.
Interestingly, the results from the current study are, in fact, in agreement with the results observed by Stockholm and Morris (20), which to the authors' knowledge, is the only previously published investigation of in-game HR during actual competitive baseball pitching. These researchers observed an in-game %HRmax value of 87%, which is similar to the mean in-game %HRmax observed in the current study (84.8%). Taken together, these results suggest that the physiological intensity of baseball pitching may be influenced by the psychological demands associated with actual in-game competition, as the in-game %HRmax values associated with Stockholm and Morris (20) and the current study were notably higher than those observed during simulated games and bullpen sessions. However, Stockholm and Morris (20) collected data from one baseball pitcher over the course of a single 9-inning game, whereas the current study collected data from a total of 682 innings. In addition, the subject used by Stockholm and Morris (20) was a collegiate-level starting pitcher and not a professional-level starting pitcher. Nevertheless, the results of the current study and that of Beiser et al. (2) and Stockholm and Morris (20), suggest that baseball pitching is primarily an anaerobic task.
The results of the simple effects from the current study also suggest that the in-game physiological intensity was significantly higher during the first 2 innings and that this in-game physiological intensity decreased across innings (Table 2). However, this change in physiological intensity was only apparent during home starts and not away starts. For example, the mean in-game %HRmax during home starts declined 4.1% from the first to the sixth innings (87.3 vs. 83.2%, respectively). This suggests that although the intensity level of baseball pitching seems to be anaerobic in nature, this intensity level also seems to be moderated by game location.
Furthermore, due to the previously established home field advantage phenomenon in athletics (14) and the direct link between mental stress and HR responses (3,4,25), it was hypothesized that various psychological factors associated with playing on the road would alter the mental stress during pitching, which would in turn result in a greater observed physiological intensity during away games. As such, it was hypothesized that the in-game %HRmax would be significantly higher among away games when compared with home games. Although a significant interaction effect between game location and inning was identified, examination of the simple effects of game location suggested that a statistically significant difference in %HRmax between home and away games is only apparent in the first inning (Figure 1). Moreover, this simple effect indicated that the in-game %HRmax in the first inning was actually significantly higher during home games than away games, which is not in agreement with the previously stated hypothesis.
In addition, although it is possible that the psychological stressors associated with the game location may influence the in-game HR responses of baseball starting pitchers, these factors seem to be inning dependent and thus may substantially impact the first inning of a game but diminish during the course of the game. This observation also coincides with the identified changes in-game %HRmax decreasing across innings among home starts. As such, the mental stress associated with the beginning of a home game may influence the physiological intensity of the first 2 innings, but this stress may diminish during the course of the game, which results in a decreased physiological intensity across innings. Therefore, future research should investigate the possible link between the psychological stressors associated with competitive baseball pitching and in-game HR responses, particularly during the beginning of the game, and compare these potential links between home and away games.
It should be noted that although all HR data were normalized to each pitcher's age-predicted HRmax, individual variability in %HRmax data still exists across pitchers (Table 1). As such, the differences in total number of innings pitched across pitchers may have influenced the results of the current study. In addition, the total number of innings pitched decreased across innings as well (Table 2). Thus, although normal distribution and equal variances were observed across all analyzed %HRmax data, it is still possible that the limited amount of data available during the fifth and sixth innings may have also influenced the results of the current study. Finally, it should be noted that although a medium effect size (η2p = 0.079) was observed in the omnibus interaction effect, and a large effect size (η2p = 0.202) was observed in the follow-up tests for the simple effects of inning, only a small effect size (η2p = 0.037) was observed in the follow-up tests for the simple effects between home and away starts in the first inning. As such, the practical implications of this statistically significant difference in %HRmax between game locations remain unknown.
In conclusion, the results of the current study suggest that the physiological demands associated with in-game baseball pitching among professional starting pitchers are anaerobic in nature. In addition, although this in-game intensity level seems to decrease across innings, the in-game intensity level of these competitive games are still much higher than the intensity during the simulated games or bullpen sessions previously examined in the literature. Furthermore, the results of the current study also suggest that game location influences the HR responses of the pitchers. As such, it is possible that the psychological aspects of pitching at home (vs. on the road) may influence the physiological intensity levels observed during the course of the game.
To prescribe training programs specific to the task demands of baseball pitching, the physiological intensity of this task must be appropriately characterized. Although it is a long-held belief that aerobic conditioning is an important element of developing a pitcher's baseline stamina (12), the results of the current study suggest that pitching is also a highly anaerobic task for professional baseball starting pitchers. When coupled with the inherent short duration and repetitive nature of pitching (18), strength and conditioning professionals should be sure to prescribe exercises that emphasize anaerobic conditioning when developing training programs for professional baseball starting pitchers. For example, potential exercises may include interval training, sprints, and other high-intensity exercises that are commonly recommended and used to target a pitcher's anaerobic energy systems (i.e., ATP-PC and glycolytic pathways) (6,7,15,19,21,22).
The authors acknowledge the support of the Milwaukee Brewers organization; in particular, the staff and players of the Wisconsin Timber Rattlers. No authors declare any conflict of interest.
1. Achten J, Jeukendrup AE. Heart rate monitoring: Applications and limitations. Sports Med 33: 517–538, 2003.
2. Beiser EJ, Szymanski DJ, Brooks KA. Physiological responses to baseball pitching during a simulated and intrasquad game [abstract]. J Strength Cond Res 26: S80, 2011.
3. Carter JR, Kupiers NT, Ray CA. Neurovascular responses to mental stress. J Physiol 564: 321–327, 2005.
4. Charkoudian N, Wallin BG. Sympathetic neural activity to the cardiovascular system: Integrator of systemic physiology and interindividual characteristics. Compr Physiol 4: 827–850, 2014.
5. Cornell DJ, Flees RJ, Caplinger RA, Seligman JR, Paxson JL, Davis NA, Ebersole KT. Influence of home and away starts on in-game heart rate responses among professional baseball starting pitchers [abstract]. J Strength Cond Res 30: S76–S77, 2016.
6. Crotin R. Game speed training in baseball. Strength Cond J 31: 13–25, 2009.
7. Crotin RL. A collaborative approach to prevent medial elbow injuries in baseball pitchers. Strength Cond J 33: 1–24, 2011.
8. Crotin RL, Kozlowski K, Horvath P, Ramsey DK. Altered stride length in response to increasing exertion among baseball pitchers. Med Sci Sports Exerc 46: 565–571, 2014.
9. Fleisig GS, Barrentine SW, Escamilla RF, Andrews JR. Biomechanics of overhead throwing with implications for injuries. Sports Med 21: 421–437, 1996.
10. Fortenbaugh D, Fleisig GS, Andrews JR. Baseball pitching biomechanics in relation to injury risk and performance. Sports Health 1: 314–320, 2009.
11. Hagerman P. Aerobic endurance training program design. In: NSCA's Essentials of Personal Training. (2nd ed.). Coburn J.W., Malek M.H., eds. Champaign, IL: Human Kinetics, 2012. pp. 389–409.
12. House T. Aerobic and anaerobic conditioning. In: Fit to Pitch. Champaign, IL: Human Kinetics, 1996. pp. 55–64.
13. Huck SW. Two-way analyses of variance. In: Reading Statistics and Research. (6th ed.). Boston, MA: Pearson, 2012. pp. 276–311.
14. Jamieson JP. The home field advantage in athletics: A meta-analysis. J Appl Soc Psychol 40: 1819–1848, 2010.
15. Kritz M, Mamula R, Messey K, Hobbs M. In-season strength and conditioning programming for collegiate baseball pitchers: A unified approach. Strength Cond J 30: 59–69, 2008.
16. Nevill AM, Holder RL. Home advantage in sport: An overview of studies on the advantage of playing at home. Sports Med 28: 221–236, 1999.
17. Potteiger JA, Blessing DL, Wilson GD. The physiological responses to a single game of baseball pitching. J Appl Sport Sci Res 6: 11–18, 1992.
18. Potteiger JA, Wilson GD. Training the pitcher: A hypothetical model. NSCA J 11: 27–31, 1989.
19. Potteiger JA, Wilson GD. Training the pitcher: A physiological perspective. NSCA J 11: 24–26, 1989.
20. Stockholm A, Morris HH. A baseball pitcher's heart rate during actual competition. Res Q 40: 645–649, 1969.
21. Szymanski DJ. Collegiate baseball in-season training. Strength Cond J 29: 68–80, 2007.
22. Szymanski DJ. Physiology of baseball pitching dictates specific exercise intensity for conditioning. Strength Cond J 31: 41–47, 2009.
23. Szymanski DJ, Myers RL. Heart rate response in collegiate baseball pitchers while pitching and conditioning [abstract]. J Strength Cond Res 21: e28, 2007.
24. Van Guilder GP, Janot JM. Acute and chronic cardiorespiratory responses to exercise. In: Exercise Physiology. (1st ed.). Porcari J., Bryant C., Comana F., eds. Philadelphia, PA: F.A. Davis, 2015. pp. 196–228.
25. Wahlström J, Hagberg M, Johnson PW, Svensson J, Rempel D. Influence of time pressure and verbal provocation on physiological and psychological reactions during work with a computer mouse. Eur J Appl Physiol 87: 257–263, 2002.
26. Warren CD, Szymanski DJ, Landers MR. Effects of three recovery protocols on range of motion, heart rate, rating of perceived exertion, and blood lactate in baseball pitchers during a simulate game. J Strength Cond Res 29: 3016–3025, 2015.