Secondary Logo

Journal Logo

Correlations Between Injury, Training Intensity, and Physical and Mental Exhaustion Among College Athletes

Vetter, Rheba E; Symonds, Matthew L

Journal of Strength and Conditioning Research: March 2010 - Volume 24 - Issue 3 - p 587-596
doi: 10.1519/JSC.0b013e3181c7c2eb
Original Research
Free

Vetter, RE and Symonds, ML. Correlations between injury, training intensity, and physical and mental exhaustion among college athletes. J Strength Cond Res 24(3): 587-596, 2010-The primary purpose of this research was to obtain information concerning injury incidence and perceptions of training intensities and fatigue levels among college athletes via a survey study. A second purpose was to illuminate correlations between the collected data. This study employed an investigator-designed survey instrument administered to 411 NCAA Division II male and female athletes, with 149 completed responses. The survey included 3 themes: injury incidence, training intensity, and physical and mental exhaustion. Men and women spent 4.5 days per week training using moderate- and high-intensity levels. Fifty percent of the total number of athletes reported chronic injury. During the competition season, physical exhaustion occurred “frequently” 30.86 and 23.53% of the time with men and women, respectively. In the noncompetition season, physical exhaustion was “frequently” experienced 19.75 and 17.65% of the time among men and women, respectively. Statistically significant correlations (p < 0.05) were found with acute injury for men and chronic injury for women. Also, training intensity levels and physical and mental exhaustion for men and women were statistically significant. The current investigators found the training involved 2-3 hours of moderate to high intensity 4.5 days per week both during competition and noncompetition; women and men spent 2-3 hours of light intensity 1.31 and 1.45 days per week, respectively. Women and men in addition to training, engaged in 3.78 and 4.43 hours of leisure physical activity per week. The investigators recommend tapering, periodization, and rest to help avoid overuse syndrome, overreaching, and overtraining that leads to excessive physical and mental exhaustion and injury.

Health, Physical Education, Recreation, and Dance Department, Northwest Missouri State University, Maryville, Missouri

Address correspondence to Rheba E. Vetter, rvetter@nwmissouri.edu.

Back to Top | Article Outline

Introduction

Enhancement of competitive athletic performance while avoiding injury has been a major goal of training programs. Thus, the pursuit of an optimal physical training program for competitive athletes has been a focus of exercise science researchers for decades. Improved physical performance has resulted from more effective training practices involving the manipulation of intensity (11,14,24), frequency (5,7,12,16,17,22,30), and volume (2,13,19,20), and mode (8-10), periodization (4,25,27), and taper (1,23,24) models.

To illuminate the optimal amount of training intensity, volume, and frequency, Peterson et al. (25) found via a meta-analysis using 37 studies, the best strength gains among athletes resulted by training muscle groups twice weekly at a mean of 85% one repetition maximum (1RM) for 8 sets per muscle group; no mention was made concerning the number of repetitions per set. They also noted decreases in strength when using more than 8 training sets. In addition, they found minimal strength gains when training with 1-3 sets of intensities at 50-70% of a 1RM.

Rhea and Alderman's (27) meta-analysis involving periodized and nonperiodized strength and power training programs elicited that periodized training programs enhanced strength and power better than nonperiodized training programs. Periodized training allowed for strength and power gains elicited from “…higher intensities and volumes without overtraining” (p. 416). This meta-analysis also showed the greatest moderating factors were the age in populations ≤55, the training status of untrained vs. trained or elite athletes, and the program length. To further support the argument for periodized training models, Buford et al. (4) compared 3 periodization models, linear progression, daily undulating periodization (DUP), and weekly undulating periodization (WUP), in recreationally trained male and female participants. The training program lasted 9 weeks, and everyone trained 3 times weekly with volume and intensity equated across the duration of the study. All groups increased bench press and leg press strength over the 9 weeks; however, DUP had lower percent changes and higher rating of perceived exertion (RPE) values, and the WUP had slightly greater strength gains and lower RPE scores.

Manipulation of the intensity, frequency, and volume training variables in tapering models has been observed (1,23,24). Bosquet's (1) meta-analysis elicited a tapering strategy for decreasing intensity and volume 41-60% over a 2-week period. These studies offer information toward designing training programs that may enhance mental and physical functions by forestalling fatigue, which leads to decreased performance and increases of chronic injury.

Although research has been conducted to ascertain the optimal amount for each training variable, there has been a paucity of studies linking information from the research to what is actually practiced among collegiate sports programs. Thus, the primary purpose of this research was to obtain information concerning injury incidence, and perceptions of training intensities and fatigue levels among college athletes via a survey study. A second purpose was to illuminate correlations between the collected data.

Back to Top | Article Outline

Methods

Experimental Approach to the Problem

This study employed an original survey instrument, designed by the current investigators. The survey instrument was divided into the following sections: (a) demographic information, (b) training frequency, (c) training intensity, (d) injury incidence, and (e) feelings of physical exhaustion, mental exhaustion, and disinterest or apathy (Table 1). Height, weight, and age were collected as continuous data. The remaining questions on the instrument used categorical responses.

Table 1

Table 1

Table 1

Table 1

Back to Top | Article Outline

Subjects

The subjects for this study were student athletes at an NCAA Division II cooperating institution sponsoring 16 sports (Table 2). The 411 students coded as athletes in the institution's data management system were invited to participate in the study.

Table 2

Table 2

Back to Top | Article Outline

Procedures

The instrument was electronically administered in the fall of 2007 by an independent third party on the campus of the cooperating institution. Subsequently, those student athletes not initially responding were sent follow-up notification and a second invitation to participate. Data from the survey were returned to the investigators in summary format by the third party before analyses. These procedures protected the anonymity of, and allowed for the voluntary participation of, the respondents. All procedures were approved by the Institutional Review Board.

Back to Top | Article Outline

Statistical Analyses

Both descriptive and Pearson product-moment correlation data analysis techniques were employed. The significance level was established at 0.05.

Back to Top | Article Outline

Results

A total of 411 electronic surveys were sent to student athletes. Completed instruments totaled 149 for a return rate of 36.25%. Data analyses began by collecting the demographic profile of the respondents (Table 2). Investigators then compiled and analyzed descriptive statistics among 3 themes from the survey: injury incidence, training intensity, and mental and physical exhaustion (Table 3). Next, investigators examined correlations between the same 3 themes (Tables 4 and 5). Collected data revealed several slight to moderate statistically significant correlations.

Table 3

Table 3

Table 4

Table 4

Table 5

Table 5

Back to Top | Article Outline

Descriptive Analyses

Descriptive statistics were compiled in the study for training frequencies, leisure time physical activity hours, and the intensity of training sessions (Table 3). Both male (mean = 5.56) and female (mean = 5.10) college athletes at the cooperating institution trained a similar number of days per week during the competition season. Men (mean = 4.98) and women (mean =4.31) also trained a comparable number of days per week during the noncompetition seasons. During the competition season, athletes in both genders trained a similar number of hours per day (male mean = 2.51; female mean = 2.93). Furthermore, men trained an average of 2.14 hours per day, and women trained an average of 2.93 hours per day during the noncompetition season. In addition to scheduled training times, both male athletes (mean = 3.78) and female athletes (mean = 4.43) spent a similar number of hours per week participating in leisure-time physical activity. The number of competitions for men and women in crosscountry and outdoor track was 8 and 14, respectively.

Thirty-eight women (56%) reported experiencing a chronic injury in the past 12 months, whereas 26 (38%) experienced an acute injury during the same time frame. Of the men in the study, 36 (44%) reported a chronic injury in the past year, whereas 37 (46%) experienced an acute injury.

Furthermore, the self-reported intensity type of training sessions was reported by athletes. Intensity type was categorized into light intensity, moderate intensity, and vigorous intensity (Table 3).

Next, the investigators compiled the reports of physical and mental exhaustion for male and female athletes during both the competition and noncompetition seasons (Table 6). Physical and mental exhaustion responses were converted to percentages by the investigators (Table 7).

Table 6

Table 6

Table 7

Table 7

Back to Top | Article Outline

Negative Correlations

Among women, data analyses revealed a statistically significant negative relationship between chronic injury incidence and noncompetitive season physical exhaustion, r (66) = −0.33, p < 0.01. For men, incidence of acute injury was negatively related to vigorous intensity training r (79) = −0.22, p < 0.05. No other statistically significant correlations for injury incidence were uncovered (Tables 4 and 5).

Light-intensity training was negatively related to 3 other variables in the study (Tables 4 and 5). A negative relationship existed between light-intensity training and noncompetitive season physical exhaustion, r (66) = −0.32, p < 0.01, among women. For men, negative relationships existed between light-intensity training and vigorous-intensity training, r (79) = −0.23, p < 0.05. A relationship between light-intensity training and competitive season physical exhaustion was also revealed for male athletes, r (79) = −0.40, p < 0.01.

Moderate-intensity training was negatively related to 3 variables in the study, 3 for men and 1 for women (Tables 4 and 5). The moderate-intensity relationships for men were between (a) vigorous intensity, r (79) = −0.25, p < 0.05, (b) competitive season physical exhaustion, r (79) = −0.23, p < 0.05, and (c) noncompetitive season physical exhaustion, r (79) = −0.34, p < 0.01. Women displayed a relationship between moderate-intensity training and vigorous-intensity training, r (66) = −0.48, p < 0.01.

Noncompetition season mental exhaustion was negatively related to chronic injury for women, r (66) = −0.379, p < 0.01, and to light-intensity training for men r (79) = −0.245, p < 0.05. Competition season mental exhaustion was also negatively correlated to acute injury for men r (79) = −0.315, p < 0.01 (Tables 6 and 7).

Back to Top | Article Outline

Positive Correlations

Vigorous-intensity training was positively correlated to competitive season physical exhaustion for men, r (79) = 0.57, p < 0.01, and noncompetitive season physical exhaustion for women, r (66) = 0.24, p < 0.05. Noncompetition season physical exhaustion was positively correlated to competition season physical exhaustion for men, r (79) = 0.43, p < 0.01 (Tables 6 and 7).

Competition season mental exhaustion was positively correlated to 3 variables for men: vigorous-intensity training, r (78) = 0.421, p < 0.01, competition season physical exhaustion, r (78) = 0.456, p < 0.01, and noncompetition physical exhaustion, r (78) = 0.268, p < 0.05. Among women in the study, competition mental exhaustion was related to competition season physical exhaustion, r (66) = 0.666, p < 0.01 (Tables 6 and 7).

Finally, noncompetition season, mental exhaustion was positively correlated to 3 variables in the study, 1 for women and 2 for men. Women with higher levels of mental exhaustion during their noncompetition season also indicated higher levels of competition season mental exhaustion, r (66) = 0.335, p < 0.01. Men with higher levels of noncompetition season mental exhaustion indicated higher levels of noncompetition physical exhaustion, r (78) = 0.488, p < 0.01, and competition season mental exhaustion, r (78) = 0.302, p < 0.01 (Tables 6 and 7).

Back to Top | Article Outline

Discussion

The 2 purposes of this research were to obtain information concerning injury incidence, and perceptions of training intensities and fatigue levels among college athletes in efforts to illuminate correlations between the collected data. Through the researcher-designed survey, the investigators collected information for demographics; training frequencies; perceived intensities; injury incidence; and feelings of physical exhaustion, mental exhaustion, and disinterest or apathy. Much of the collected information seems like common sense when viewed through the lens of previous research involving intensity, frequency, and volume.

Both male and female athletes in the current study reported training frequencies of 5-5.5 days per week during competition season and 4.5-5 days during noncompetition season. Hoffman et al. (16) studied training frequency among football players, and their findings indicate that 5 days per week produced upper and lower body strength gains, running endurance, and body composition better than the 3- or 6-day groups; improvements in the 4-day group were similar to the 5day group except that no significant improvement in bench press occurred. They also concluded that lack of significant improvements over the 10-week study in the 3- and 6-day groups indicated evidence of overtraining, because these groups performed a greater volume than the 4- or 5-day groups. Wirth and Schmidtbleicher (30) found strength increased 2.7, 7.3, and 12.8% in athletes training 1, 2, and 3 days per week, respectively. These investigators suggested that 2 training sessions were optimal because of other training components included in a weekly program. The current study did not differentiate day-to-day training activities within the survey questions.

Men in the current study reported performing 1.46, 2.19, and 2.48 days of light-, moderate-, and vigorous-intensity training weekly, respectively. The women trained, respectively, 1.31, 2.32, and 2.22 days with light-, moderate-, and vigorous-intensity weekly. In relation to the results of the following studies, perhaps the men and women in the current research used more high-intensity training rather than moderate zones. Gonzalez-Badillo et al. (14) studied strength gains in competitive weightlifters after 10 weeks of training 4-5 days per week. They found that moderate volumes of high relative intensity (78-79%) produced greater performance gains than the low (77-78%) and high (80-81%) volumes of similar relative intensity; high intensity consisted of 182 repetitions with resistance greater than 90% of 1RM, moderate intensity used 91 repetitions with weight greater than 90% of 1RM, and low-intensity performance included 4 repetitions with resistance greater than 90% 1RM. High was less effective than low. Esteve-Lanao et al. (11) compared 2 5-month endurance training programs involving low-intensity zone 1 (below ventilatory threshold) and moderate-intensity zone 2 (between ventilatory threshold and respiratory compensation threshold) and high-intensity zone 3 (above respiratory compensation threshold; ≥ 90% O2max). During competition, both groups performed high intensity 2 times weekly, and the remaining training was either in zone 1 or zone 2, dependent on their assigned group. Also, both groups included 1 weight training session per week with 1-2 sets of 60% 1RM. Posttraining performance time improved significantly for both groups but was greater for the group spending more time in zone 1. Their results indicated that training intensity was critical when volume and load were constant; a faster racing pace was elicited among trained endurance athletes with 80% of training in zone 1, 12% in zone 2, and 8% in zone 3. Thus, according to research, it appeared that a greater proportion of moderate intensity in either aerobic or anaerobic training produced enhanced performance; of particular interest noted concerning intensity was the fact that the high anaerobic and high aerobic groups were less effective than the moderate- and low-intensity groups.

Athletes in the current study reported perceived physical and mental exhaustion for both the competition and noncompetition seasons: rarely, sometimes, or frequently (Tables 6 and 7). Growing concern exists about the lack of time off or significantly reduced training, the related levels of exhaustion, and the ultimate impact on performance and burnout. Sport psychology authors have noted both mental and physical exhaustion as signs of overtraining and burnout and causes for decreases in athletic performance (6,28,29). Moreover, related research exists regarding the unexplained underperformance syndrome, which contains physical and mental exhaustion components (3,26). Also, implementing systematic recovery periods to maximize performance or developing balance between training and recovery has also been a topic of discussion (15,18). The findings of the current study echo previous research, because statistically significant relationships were uncovered related to mental exhaustion, both during the competition and noncompetition seasons to injury, training intensity, and physical exhaustion.

Systematic protocols using taper strategies offer methods to avoid overuse syndromes that may lead to injury. Results from taper research indicate that changes in training intensity produce the greatest differences in training results, and alterations in volume and frequency play a lesser role in performance maintenance or improvement. Mujika and Padilla (24) state the optimal tapering strategies to minimize fatigue and maximize performance among athletes involve a 60-90% volume reduction, no intensity changes, and frequency should be maintained above 80% within a nonlinear individualized program design. In the current study, 56 and 44% of the women and men, respectively, experienced chronic injuries within a 12-month period. Chronic injuries can be a result of overuse leading to overreaching or overtraining that may take days, weeks, or months for recovery.

The male athletes in this study reported physical exhaustion during both the competition (59.26% sometimes, 30.86% frequently) and the noncompetition season (55.56% sometimes, 19.75% frequently). The men also trained in the moderate- or vigorous-intensity range 2.20 (±1.47) and 2.48 (±1.59) days per week. Given that 44% of the men reported chronic injuries, one might question whether overreaching or overtraining was occurring even though there were insignificant correlations between exhaustion and injury, and physical intensity and injury (Table 5).

Similarly, 56% of the female athletes reported chronic injuries with physical exhaustion occurring 66.18% sometimes and 23.53% frequently during competition and 66.18% sometimes and 17.65% frequently during noncompetition (Tables 4 and 7). Thus, once again, even though there was actually a negative correlation, one might assume the intensity of training added to injury and then the training lessened or ceased.

Periodized training program designs have also been used to enhance performance gains and diminish fatigue levels, which leads to overreaching or overtraining over time. In general, Rhea and Alderman (27) found no differences between genders, ages 55 and younger experienced greater responses than older populations, and untrained populations had greater responses than athletes and trained populations. Their meta-analysis also revealed that training periods less than 8 weeks resulted in lower adaptation responses; training 9-20 weeks was optimal with apparent plateaus for programs lasting more than 20 weeks. The research of Buford et al. (4) indicated a WUP model that modified volume or intensity on a weekly basis was most beneficial for strength development and lowering perceived exertion; RPE was examined throughout their study as a valid measure to quantify intensity as related to “…impending overtraining syndrome.” (p. 1246). The current research did not address whether or what type periodization was used.

One manner periodization was used was to reconfigure the resistance loads within a program. Brandenburg and Docherty (2) found the reduced load protocol produced greater fatigue, as measured by maximal isometric force and lactic acid, than the constant load protocol. The constant intensity load used 77.8% of 1RM for each set, whereas the reduced load went from 81% intensity for set one down to an average of 74.2% across all sets, which enabled more repetitions to be completed for the reduced load protocol. Both protocols produced similar strength gains after the 8-week program. No effort in the current research was made concerning specific daily training activities.

Several limitations with the current study exist. One limitation to the current study is a lack of specificity in identifying the training components of weight training, aerobic conditioning, and sport specific activities. Of particular interest for designing training programs is noting the cause of the greatest fatigue over the course of a week. If a particular program component is cited as a main cause for fatigue then that variable could be further modified by periodization or tapering protocols. Another limitation is the generalization of training information with regard to intensities and volumes. Knowledge of intensities and numbers of sets and repetitions during daily weight training, or the amount of time in active sport specific practice is important for ascertaining specifics related to fatigue.

In summary, the primary purpose of this research was to obtain information concerning injury incidence and perceptions of actual training intensities and fatigue levels among college athletes via a survey study. A second purpose was to illuminate correlations between the collected data.

Among both men and women approximately 4.5 days per week in training is spent performing moderate and high levels of intensity. First-hand experience with any athlete on campus reveals that these individuals are frequently tired. As one might expect with college athletes, frequency of training occurs roughly 5 days per week, not to mention any leisure time spent participating in physical activity.

It is felt by the investigators that the injury prevalence is high with 50% of the total number of athletes who responded to this survey reporting chronic injury. This is of importance because the causes of chronic injury are complex and individualized, varying from overuse, overreaching and overtraining to rehabilitation issues post-acute injuries and during chronic injury.

Perceived physical exhaustion occurred “frequently” 30.86 and 23.53% of the time with men and women, respectively, during the competition season. Only 19.75 and 17.65% of the time was physical exhaustion “frequently” experienced during noncompetition among men and women, respectively.

In conclusion, the investigators found significant negative correlations between chronic injury incidence and noncompetitive season physical exhaustion among women. For men, acute injury incidence was negatively related to vigorous-intensity training. Light-intensity training was negatively related to noncompetitive season physical exhaustion among women and vigorous-intensity training for men. A relationship between light-intensity training and competitive season physical exhaustion was also revealed for male athletes. Moderate-intensity training for males was negatively related to vigorous-intensity training, competitive season physical exhaustion, and noncompetitive season physical exhaustion. Moderate-intensity training for females was negatively related to vigorous-intensity training. Significant positive correlations included vigorous-intensity training and competitive season physical exhaustion for men and between noncompetitive season physical exhaustion for women. Finally, noncompetition season physical exhaustion was positively correlated to competition season physical exhaustion for men.

Back to Top | Article Outline

Practical Applications

Coaches and trainers could plan more moderate zoned training time each week during competition season because the current investigators found the training was predominantly 2-3 hours of moderate to high intensity 4.5 days per week both during competition and noncompetition. Especially for highly active participants during competition season, where the competition event elicits higher intensity than the weekly training days, moderate training levels in the 77-80% (2,14) intensity with tapering of 60-90% (24) is recommended. Because there does not seem to be a real “off season” because athletes train almost 12 months during the year, tapering, periodization, and rest are extremely important to help avoid overreaching and overtraining leading to excessive physical and mental exhaustion and injury.

One way to avoid overuse, overreaching, and overtraining is through the daily training log. Daily RPE for each exercise and activity can be recorded and tracked to forestall the onset of overtraining. Of particular interest would be to note the intensity, volume, and related RPE of each exercise or activity. Acute mental and physical fatigue levels and delayed onset soreness and mood states provide information for individualization. With the ultimate goal of performance enhancement and injury prevention, it is important to consider daily to weekly to monthly fluctuations in training components for individual athletes.

Future research collecting specific data on each athlete's daily training activities involving the intensities, volumes, frequencies, sport-specific exercise, and the RPE scores related to each daily activity can further facilitate both generalized and individualized training protocols. Also, recognizing the onset of chronic injury within each training season could illuminate the patterns of activities leading up to chronic injury for that individual; this might help the person avoid those same patterns in the future.

Back to Top | Article Outline

Acknowledgments

We would like to thank Mr. Paul Klute for electronically administering the survey used for this research study.

Back to Top | Article Outline

References

1. Bosquet, L, Montpetit, J, Arvisais, D, and Mujika, I. Effects of tapering on performance: A meta-analysis. Med Sci Sports Exerc 39: 1358-1365, 2007.
2. Brandenburg, J and Docherty, D. The effect of training volume on the acute response and adaptations to resistance training. Int J Sports Physiol Perform 1: 108-121, 2006.
3. Budgett, R. Overtraining and chronic fatigue: The unexplained underperformance syndrome (UPS). Int SportMed J 1: Retrieved August 4, 2008 from http://web.ebscohost.com/ehost/pdf?vid=16&hid=15&sid=50380b31-785b-45de-8954-7145ac986b80%40sessionmgr3, 2000.
4. Buford, TW, Rossi, SJ, Smith, DB, and Warren, AJ. A comparison of periodization models during nine weeks with equated volume and intensity for strength. J Strength Cond Res 21: 1245-1250, 2007.
5. Carpenter, DM, Graves, JE, Pollock, ML, Leggett, SH, Foster, D, Holmes, B, and Fulton, MN. Effect of 12 and 20 weeks of resistance training on lumbar extension torque production. Phys Ther 71: 36-44, 1991.
6. Cox, RH. Sport Psychology: Concepts and Applications. New York, NY: McGraw-Hill, 2007.
7. DeRenne, C, Hetzler, RK, Buxton, BP, and Ho, KW. Effects of training frequency on strength maintenance in pubescent baseball players. J Strength Cond Res 10: 8-14, 1996.
8. Dodd, DJ and Alvar, BA. Analysis of acute explosive training modalities to improve lower-body power in baseball players. J Strength Cond Res 21: 1177-1182, 2007.
9. Drinkwater, EJ, Lawton, TW, Lindsell, RP, Pyne, DB, Hunt, PH, and McKenna, MJ. Training leading to repetition failure enhances bench press strength gains in elite junior athletes. J Strength Cond Res 19: 382-388, 2005.
10. Drinkwater, EJ, Lawton, TW, McKenna, MJ, Lindsell, RP, Hunt, PH, and Pyne, DB. Increased number of forced repetitions does not enhance strength development with resistance training. J Strength Cond Res 21: 841-847, 2007.
11. Esteve-Lanao, J, Foster, C, Seiler, S, and Lucia, A. Impact of training intensity distribution on performance in endurance athletes. J Strength Cond Res 21: 943-949, 2007.
12. Faigenbaum, AD, Milliken, LA, Loud, RL, Burak, BT, Doherty, CL, and Westcott, WL. Comparison of 1 and 2 days per week of strength training in children. Res Quart Exerc Sport 73: 416-424, 2002.
13. Gonzalez-Badillo, JJ, Gorostiaga, EM, Arellano, R, and Izquierdo, M. Moderate resistance training volume produces more favorable strength gains than high or low volumes during a short-term training cycle. J Strength Cond Res 19: 689-697, 2005.
14. Gonzalez-Badillo, JJ, Izquierdo, M, and Gorostiaga, EM. Moderate volume of high relative training intensity produces greater strength gains compared with low and high volumes in competitive weightlifters. J Strength Cond Res 20: 73-81, 2006.
15. Halson, SL and Jeukendrup, AE. Does overtraining exist? An analysis of overreaching and overtraining research [electronic version]. Sports Med 34: 967-981, 2004.
16. Hoffman, JR, Kraemer, WJ, Fry, AC, Deschenes, M, and Kemp, M. The effects of self-selection for frequency of training in a winter conditioning program for football. J Appl Sport Sci Res 4: 76-82, 1990.
17. Hunter, GR. Changes in body composition, body build and performance associated with different weight training frequencies in males and females. Natl Strength Cond Assoc J 7: 26-28, 1985.
18. Kellman, M and Gunther, K. Changes in stress and recovery in elite rowers during preparation for the Olympic Games. Med Sci Sports Exerc 35: 676-683, 2000.
19. Kelly, SB, Brown, LE, Coburn, JW, Zinder, SM, Gardner, LM, and Nguyen, D. The effect of single versus multiple sets on strength. J Strength Cond Res 21: 1003-1006, 2007.
20. Kemmler, WK, Lauber, D, Engelke, K, and Weineck, J. Effects of single vs. multiple set resistance training on maximum strength and body composition in trained postmenopausal women. J Strength Cond Res 18: 689-694, 2004.
21. McLester, JR Jr, Bishop, P, and Guilliams, ME. Comparison of 1 day and 3 days per week of equal-volume resistance training in experienced subjects. J Strength Cond Res 14: 273-281, 2000.
22. Mostardi, RA and Campbell, TA. Effects of training once vs. twice per day and improvement in maximal aerobic power. Ohio J Sci 81: 207-211, 1981.
23. Mujika, I, Goya, A, Ruiz, E, Grijalba, A, Santisteban, J, and Padilla, S. Physiological and performance responses to a 6-day taper in middle-distance runners: Influence of training frequency. Int J Sports Med 23: 367-373, 2002.
24. Mujika, I and Padilla, S. Scientific bases for precompetition tapering strategies. Med Sci Sports Exerc 35: 1182-1187, 2003.
25. Peterson, MD, Rhea, MR, and Alvar, BA. Maximizing strength development in athletes: A meta-analysis to determine the dose-response relationship. J Strength Cond Res 18: 377-382, 2004.
26. Pollman, R and Houlahan, K. A cumulative stress and training continuum model: A multidisciplinary approach to unexplained underperformance syndrome. Res Sports Med [electr vers] 12: 301-316, 2004.
27. Rhea, MR and Alderman, BL. A meta-analysis of periodized versus nonperiodized strength and power training programs. Res Quart Exerc Sport 75: 413-422, 2004.
28. Weinberg, RS and Gould, D. Foundations of Sport and Exercise Psychology (4th ed.). Champaign, IL: Human Kinetics, 2007.
29. Williams, JM. Applied Sport Psychology: Personal Growth to Peak Performance. New York, NY: McGraw-Hill, 2006.
30. Wirth, K and Schmidtbleicher, D. The development of 1 repetition maximum (1RM) depending on the training frequency during a hypertrophy training program with high performance athletes. Isokinetics Exerc Sci 10: 58-59, 2002.
Keywords:

tapering; overuse syndrome; overreaching; overtraining; performance enhancement; periodization

© 2010 National Strength and Conditioning Association