The Fitness-Fatigue Model Revisited: Implications for Planning Short- and Long-Term Training

Loren Z.F. Chiu, MS, CSCS Musculoskeletal Biomechanics Research Laboratory University of Southern California

Jacque L. Barnes Human Performance Laboratories University of Memphis

Keywords: organization of training; periodization; overreaching; athletic performance.

ELITE ATHLETIC PERFORMANCE stage, where positive adaptations sponses. The state of the organism is dependent on a systemized occur, returning the organism to without training is the baseline training program. The general homeostasis and possibly into a level, which represents the indi- adaptation syndrome (GAS) was higher state, known as supercom- vidual’s general fitness. Training the original model from which pe- pensation. The exhaustion stage results in 2 after-effects, which riodization was designed (67). The occurs when the imposed stress is can positively or negatively influ- GAS describes the physiological greater than the adaptive reserves ence performance: fitness and fa- response of an organism to stress. of the organism. This can happen tigue (Figure 1). For strength and A more comprehensive model of when the magnitude of stress is power athletes, factors that affect the physiological responses to too large or additional stressors general fitness include muscle training stimuli is the fitness-fa- occur. As the response is suppos- cross-sectional area, muscle con- tigue theory (1). In light of recent edly similar for all stressors, the tractile protein composition, and research examining resistance ex- magnitude and duration of train- muscle metabolic enzyme concen- ercise overreaching and overtraining determine the magnitude and trations (23, 24, 44, 62). For en- ing, it is prudent to review the fit- duration of adaptation. durance athletes, both cardio-res- ness-fatigue theory and determine In traditional periodization piratory factors and muscular how it can be applied to strength models, there are multiple bouts factors affect general fitness (53). and conditioning. of training, resulting in multiple Examples of these are maximal flights of alarm and resistance oxygen consumption, mitochon- ■ General Adaptation stages (63, 67). Periodically reduc- drial density, and muscle capillar- Syndrome ing volume load may prevent the ization. General fitness increases Initially described by Selye in exhaustion stage (63, 67). If the with training age; thus elite ath- 1956 (60), the GAS proposes that individual reaches the exhaustion letes have higher general fitness all stressors result in similar re- stage, overtraining occurs. than novices do. sponses. The initial response, the The fitness after-effect is a ■ alarm stage, is negative, with the Fitness-Fatigue Model positive physiological response, physiological state of the organism Proposed in 1982 by Bannister (1), whereas the fatigue after-effect is decreasing following the imposi- the fitness-fatigue model argues a negative physiological response. tion of stress. Secondary to the that different training stresses re- The interaction between these 2 alarm stage is the resistance sult in different physiological re- after-effects results in the change

42 Strength and Conditioning Journal December 2003 in performance following the stim- Down-regulation of the alpha- and physiological literature. Similarly, ulus (1, 67). It is important to note beta-receptors or decreasing the there is an absence of evidence here that the fitness-fatigue model release of catecholamines can de- supporting the single unified re- is not necessarily an alternative to crease nervous system function sponse proposed by Selye (60). the GAS, but rather a better rep- (12, 25, 28, 35). Metabolic fatigue The initial bases for the GAS are resentation of stimulus and re- is primarily due to decreased stor- the endocrine responses to stress sponse. Indeed, the resultant age and availability of energy sub- (60, 67). These endocrine respons- change in performance as de- strates (10, 25, 45, 64, 67). es, however, are not the same for scribed in this model is identical The magnitude and duration all exercise regimes. Higher-vol- to the GAS. The distinction of fit- of the after-effects is dependent on ume training results in an acute ness and fatigue after-effects, the stimulus, where Bannister (1) decrease in circulating testos- however, is important for the de- initially proposed that training im- terone, whereas higher-intensity velopment of training paradigms. pulse, an indicator of physiologi- training results in an acute in- Fitness after-effects, whether cal work, was the sole variable. In crease in circulating testosterone acute or chronic, appear to be pri- general, the fatigue after-effect is (46, 47, 49). High-volume, moder- marily neural in nature. Facilita- large in magnitude with a brief du- ate-intensity exercise increases tion of the peripheral nervous sys- ration. This results in the initial growth hormone, but low-volume, tem occurs via optimal magnitude decrease in performance (similar very high-intensity training has no and rate of activation of the neuro- to Selye’s alarm stage). The fitness growth hormone response (47, muscular complex, coactivation of after-effect has a dull magnitude, 49). Correspondingly, a brief de- intrafusal fibers, and decreased but a long duration. This mani- crease in performance can occur autogenic inhibition (20–22, fests as a long-term improvement regardless of the increase or de- 27–34, 38–41, 51, 52). Central in performance (similar to Selye’s crease in circulating hormones nervous system activity increases resistance stage). (35–38, 40, 41). The original through up-regulation of the propositions of the GAS are thus ■ alpha- and beta-receptors and Evidence of After-Effects far too simplistic to accurately de- greater catecholamine release (12). Evidence of the existence of 2 scribe the physiological response Fatigue after-effects are both after-effects, as opposed to a sin- to stimuli. neural and metabolic in nature. gle unified response, exists in the Perhaps the best evidence of fitness and fatigue after-effects is the physiological phenomenon posttetanic potentiation. Postte- tanic potentiation is the increase in muscle twitch force following voluntary or involuntary maximal contractions (9). Brown and von Euler (3) reported that successive contractions in isolated muscle preparations resulted in greater force production. Further research in animals and humans corroborated these findings, indi- cating that maximal voluntary contractions resulted in an increase in performance (9, 11, 19, 42, 57). Interestingly, individuals competing in sports respond fa- vorably, whereas recreationally trained individuals fatigued after the maximal voluntary contractions (9). Chiu et al. (9) speculated that the athletic individuals had a Figure 1. Fitness-fatigue theory. greater potentiation response (fit-

December 2003 Strength and Conditioning Journal 43 ness after-effect) and less fatigue priate measure for the training ry. The GAS theory states that compared with the recreationally stimulus. Training impulse is a total work alone, regardless of the trained individuals. measure of total work performed, magnitude of stress, is responsi- Physiologically, maximal con- and a similar measure exists for ble for the responses. In the fit- tractions cause a depletion of cre- resistance exercise, called volume ness-fatigue model, both the atine phosphate, an accumulation load (64). Volume load refers to the amount and magnitude of the of extracellular potassium, and an total kilograms of weight lifted. stimulus contributes to the post- increase in intramuscular calcium Whether training impulse (for en- exercise response. Indeed, this and hydrogen (53). These changes durance activities) or volume load distinction may demonstrate the contribute to decreased muscle (for resistance exercise), this no- complexity of the fitness-fatigue force production. Alternatively, tion that total work is the stimu- model. Absolute load, training in- maximal contractions result in lus responsible for short- and tensity, and total work appear to phosphorylation of the regulatory long-term adaptation is intellectu- have their own fitness and fatigue myosin light chain and the H-re- ally appealing. However, the re- after-effects. Therefore, the origi- flex (9, 19, 42, 57). The regulatory search by Fry et al. (12, 13, 15, 16) nal model—having 1 fitness after- myosin light chain is a protein shows that exercise with high load effect and 1 fatigue after-effect— that regulates the rate of muscle or high intensity in absence of may be misleading. There may contraction. Phosphorylation of high volume loads results in both actually be multiple fitness after- this protein increases the rate of positive and negative adaptations effects and multiple fatigue after- binding of actin and myosin, re- (45, 58). Thus for a single bout of effects (Figure 2). sulting in faster muscle contrac- exercise, absolute load, training Although each specific fitness tion (57). The H-reflex is a reflex- intensity, and total work are re- and fatigue after-effect is indepen- ive neural signal, which when sponsible for the magnitude and dent of each other, they have a cu- superimposed on voluntary mus- duration of the fitness and fatigue mulative effect. Of primary con- cle activation, increases the after-effects (4–7, 20–22, 29–32, cern is the summation of fatigue strength of the electrical impulse, 34, 40, 51, 52, 56). after-effects. Individual fatigue thus activating more motor units This important revelation il- after-effects are specific respons- (19). lustrates the differing impacts of es to stimuli; however, these re- In addition to these acute re- the GAS and fitness-fatigue theo- sponses can have a systemic ef- sponses, short-term training adaptations support the fitness- fatigue model. Fry et al. (16) found that following 3 weeks of high relative intensity resistance exercise, strength did not change, whereas speed decreased. Subjects performed near maximal lifts 3 days per week using the free-weight barbell squat. Sprint performance decreased following training, with a 10% increase in 9.1-m run time. This differential response between strength and speed occurs repeat- edly in resistance exercise overtraining studies and is supportive of different responses to stress (12, 13, 15, 16, 45, 58). ■ Stimulus and Response Bannister (1) suggested that training impulse—the product of heart rate (or exercise intensity) and exercise duration—was the appro- Figure 2. Revised fitness-fatigue theory

44 Strength and Conditioning Journal December 2003 fect, in particular affecting the im- Regardless of the training pa- of specific fitness and fatigue after- mune system. When fatigue after- rameters, adaptations in begin- effects is high. A period of training effects are small and brief, the ners performing resistance exer- involving reduced total work and systemic effect is small. However, cise include muscle hypertrophy relative intensity is required to re- stressful periods of training with- and shift of myosin heavy chain move the fatigue after-effects out sufficient recovery result in an IIb to IIa (8, 53, 55, 62). Maximal (1, 67). When applied before a accumulation of fatigue and an in- oxygen consumption, increased major competition, this phase is a crease in the systemic or main fa- mitochondrial density, and in- taper (14, 18, 27, 54, 61, 65). Al- tigue after-effect. creased capillarization result from though widely applied in coaching The existence of multiple fit- most types of endurance training circles, the acknowledgment of the ness and fatigue after-effects may (53). An explanation for the diver- delayed training effect has been explain why individual physical gence in performance adaptations missing in scientific research. qualities respond differently to between different programs is the Without a taper period, it is diffi- variations in training. For exam- rate and magnitude of adapta- cult to interpret the true impact of ple, empirical evidence in tions, rather than the type of a training program. Preliminary weightlifters finds that in periods adaptations (55). These adapta- evidence suggests 96 hours of rest of maximal strength training, ex- tions are stable and do not tend to may be necessary in recreational- plosive strength and muscular regress unless a prolonged period ly trained individuals for optimal endurance suffer. Similarly, of detraining occurs (43, 44, 48). strength performance (65). strength is impaired when the Elite athletes have developed a The period of rest required for emphasis is on explosive strength high general fitness level; thus the maximal strength and velocity (2). If different fitness after-ef- training emphasis shifts to specif- adaptations to manifest may de- fects exist for absolute strength, ic fitness adaptations. The highest pend on the nature of the training explosive strength, and muscular level of performance occurs when (59). Training involving concen- endurance, they should be spe- fatigue after-effects are minimal tric-only or eccentric-only move- cific to the mode of training best and fitness after-effects are maxi- ments requires 10–14 days of rest suited for that physical quality. mal. Mathematical functions can for optimal strength and velocity Thus when the emphasis of train- represent the fitness and fatigue adaptations. For typical eccentric- ing is on one and not the other after-effects (1, 4–7). As the after- concentric exercise, strength and physical qualities, the other spe- effects decay, they follow an as- velocity were greatest 21 days fol- cific fitness after-effects diminish ymptotic function where the after- lowing termination of training. and that specific aspect of perfor- effect approaches but does not Whether the concentric-only, ec- mance increases. reach zero. Thus it is impossible centric-only, or eccentric-concen- for fitness or fatigue to exist inde- tric exercise modes were directly ■ Implications for Training pendently. Bannister (1) proposes responsible for the different taper For novice athletes, the emphasis that it is better to have high fitness times is disputable, as eccentric- of training is on improving the with moderate fatigue, rather than concentric training would involve general fitness level. The general moderate fitness and low fatigue. roughly twice the volume load as fitness aspect of the fitness-fa- Manipulating training parameters the other modalities. Regardless, tigue theory explains why begin- can alter the magnitude and du- the major finding is in support of ners tend to respond to any type rations of these after-effects, pro- a delayed training effect. of training program. When begin- ducing the optimal level of perfor- It is rare, however, for elite ners train, general fitness adapta- mance. From the temporal pattern athletes to completely abstain tions occur without substantial of the fatigue after-effect, it is im- from training the last weeks before fitness and fatigue after-effects. portant to note that maximal per- competition. Although a drastic Novices cannot train with suffi- formance does not occur immedi- reduction in volume load occurs cient absolute load, intensity, or ately after the training phase. during these few weeks, empiri- volume to elicit large fitness and cally, intensity remains high. This ■ fatigue after-effects. Thus begin- Delayed Training Effect is especially true in elite ners adapt so that they can toler- The delayed training effect is a di- weightlifters. The brief, infrequent ate greater absolute loads, exer- rect consequence of the fitness-fa- imposition of high-intensity train- cise intensities, and training tigue model. Following a period of ing may maintain or increase the volumes. stressful training, the magnitude specific fitness after-effects with-

December 2003 Strength and Conditioning Journal 45 out substantially affecting fatigue ments may not occur due to the from excess training volume. after-effects (16, 43, 64). There- positive effect of the fitness after- Lehmann et al. (50) found perfor- fore, this period is more than sim- effects. Over time, the persistent mance impairments in overtrained ply removing the fatigue after-ef- addition of fatigue after-effects endurance athletes as much as 1 fect; this period also maximizes results in a depletion in the ath- year following reduction in train- the magnitude of the fitness after- lete’s adaptive abilities, resulting ing stress. Overtraining from in- effect. Thus, rather than taper, a in overtraining. It is here that the creased loads or training intensity more appropriate term for this GAS falls short in explaining why should resolve within a few weeks phase of training may be ramping. performance drops sharply when of rest (16, 45, 64). overtraining occurs. Following ■ ■ Short-Term Overreaching the GAS model, performance Long-Term Planning The fitness-fatigue theory and de- should decrease progressively Although it has fallen out of favor layed training effect are important with additional stressors, which among many strength and condi- to consider in planning the train- empirically is not the case. With tioning professionals, the tradi- ing of elite athletes. Elite athletes the fitness-fatigue model, fatigue tional periodization model holds can tolerate greater volume load accumulates, and at the point concepts that are still important and training intensity than when fatigue after-effects greatly for planning training programs. novices and require more stress to exceed fitness after-effects, over- Perhaps the most important is the stimulate adaptations. The fre- training occurs. inverse relationship between vol- quent imposition of these stress- We must be careful in labeling ume and intensity (63). If we re- es, however, makes the athlete overtraining, as it typically re- member that longer durations are more susceptible to overtraining. quires a prolonged period of required to overtrain and recover The need for variation in volume stressful training to reach (12, 64). from overtraining, with training load and intensity are the ratio- Coaches and sport scientists volume it would be prudent to nale behind short-term overreach- should not underestimate the only use higher training volumes ing (12, 64, 67). adaptive abilities of the human early in the training plan. Short-term overreaching is the body (14). Most individuals will Higher frequency of training, deliberate imposition of stressful never reach a true overtraining and therefore higher training vol- training for brief periods inter- state. Prior research in elite ath- ume, increases the duration of the spersed with periods of recovery letes has found an ability to toler- fatigue effect associated with a (12, 64). These stressful periods ate twofold or threefold increases single training session (4). This result in large fitness and fatigue in training volume for periods of may be tolerable early in the train- after-effects. As the duration of 1–3 weeks (14, 64). ing year when fatigue has not ac- the fitness after-effect is longer With resistance exercise, cumulated; however, if training than the fatigue after-effect, a pe- recreationally trained individuals frequency remains high through- riod of rest allows fatigue to di- are able to maintain or increase out the training year, the ability to minish while fitness remains high. strength with 3–5 d/wk of training recover is impaired (4). Reducing Stone and Fry (64) and Fry (12) with near maximal loads (>90% 1 training volume toward the mid- have proposed that this frequent repetition maximum [1RM]; 13, point of the training year will allow cycling of training and recovery 16). Velocity-related perfor- sufficient time for fatigue to di- phases is necessary to improve mances, such as sprinting, de- minish. The use of higher training performance in elite athletes. crease at this frequency and in- volume early in the training plan tensity of training. A training also results in increased adaptive ■ Overtraining frequency of 7 d/wk for 2 consec- abilities, which would be useful It is important to consider that utive weeks results in large later in the training year (14). the fitness and fatigue after-ef- strength decrements (15, 58). Intensity manipulations result fects are dynamic and not static Thus training with excessive loads in more predictable responses entities. If training occurs while results in overtraining faster than than volume manipulation, fatigue after-effects persist, addi- training with excessive volume. whether positive or negative (9, tional after-effects will superim- Similarly, overtraining result- 20, 21, 25, 29, 32, 35–38, 40, 51, pose on existing ones, exacerbat- ing from load and intensity ma- 52, 56). Thus as the competition ing the maladaptations (1). nipulations appears to resolve period nears, it is wise to reduce However, performance decre- faster than overtraining resulting training volume to avoid pro-

46 Strength and Conditioning Journal December 2003 longed fatigue after-effects while near-maximal loads lifted for mul- letes who trained twice per day addressing training intensity to tiple sets of few repetitions. Maxi- improved strength more than in- maximize the fitness after-effects. mal intensity training uses sub- dividuals who trained only once Typically, sequencing of long- maximal loads lifted with maximal per day (26). Only athletes who term training is in a multidirec- acceleration for multiple sets of low have a high level of general fitness tional fashion. With multidirec- to moderate repetitions. Maximal should perform multiple daily tional training, athletes train work training involves a high vol- training sessions. From prelimi- multiple physical qualities in the ume of lifts with submaximal loads. nary research, maximal strength same period. For elite athletes, it Maximal intensity training has training sessions precede maximal may be necessary to train in a uni- the largest fitness after-effect, intensity sessions. The large fa- directional fashion, where empha- which is of short duration (9, 19, tigue after-effect from maximal in- sis is on only 1 physical quality 34, 51, 52). Maximal work training tensity training appears to mani- during a given training period. For has the smallest fitness after-ef- fest during the session or in the example, an athlete may perform fect, yet the duration is longest intersession interval (2, 66). This a 4-week block of training focus- (25). Maximal strength training fatigue after-effect negatively af- ing on strength only (67). The uni- has a smaller fitness after-effect fects maximal strength, but not directional method usually results than maximal intensity training (9, explosive strength (2). A single in short-term overreaching of the 19, 34, 51, 52). The fatigue after- maximal intensity training session trained quality. effects are similar, with maximal results in decreased force produc- Some coaches and scientists intensity resulting in large fatigue tion during a second training ses- suggest that consecutive over- for a brief period and maximal sion 4–6 hours later. The earlier reaching phases are possible, so work resulting in low-levels of fa- training session does not affect ex- long as each phase is unidirec- tigue for a prolonged period (5–7, plosive strength or training veloc- tional and emphasizes a different 9, 17, 19, 25, 34, 51, 52, 56, 66). ity. Again, when training multiple physical quality (67). This concurs In planning a single training times per day, maximal work with the proposed revised fitness- session, maximal intensity and training occurs last. fatigue model involving multiple maximal strength training always ■ fitness and fatigue after-effects. precede maximal work. The onset Short-Term Training The fatigue after-effect specific to of fatigue with maximal work When concurrently training 1 physical quality should not training is nearly immediate, as multiple strength qualities, early hamper the performance of an- opposed to maximal intensity and in the week the emphasis should other physical quality. This ap- strength, where the fitness after- be on maximal intensity. As the plies so long as systemic mal- effect offsets fatigue (17, 25). Elite fatigue after-effect is shortest for adaptations, such as impaired athletes can perform maximal maximal intensity training, this immune system function, do not strength training before maximal arrangement has the smallest occur. Thus even with unidirec- intensity. This sequencing takes negative effect on subsequent tional sequencing, the training advantage of the posttetanic po- days of training. Additionally, plan should include brief periods tentiation phenomenon (9). Less- the large fitness after-effect may for recovery. er-trained athletes, however, positively influence subsequent should always perform maximal training days. A day emphasiz- ■ Dynamics of the Training Day intensity training before maximal ing maximal strength occurs A single training session can influ- strength training. Elite athletes after days of maximal intensity ence subsequent training sessions, may also use this sequencing. In training, so it does not negative- both positively and negatively (2, lesser-trained individuals, fatigue ly affect the maximal intensity 26, 40, 66). The effect depends on follows maximal strength training, training sessions. Similarly, the type of training performed. impairing maximal intensity per- maximal work occurs toward the From the research literature, there formance (9, 11). end of the week, closer to days of are 3 distinctive types of strength Rather than training multiple rest, which will allow fatigue to training, which have differing phys- strength qualities in a single train- recover. iological effects on the organism: ing session, dividing training into In general, training sessions maximal strength, maximal inten- multiple sessions per day may be resulting in a large fitness after-ef- sity, and maximal work (67). Maxi- appropriate. Even when total fect and a brief fatigue after-effect mal strength training involves training volume was equal, ath- should occur early in the training

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