Biochemical Foundations of Human Vital Activity - Volkov, N. I., & Nesen, E. N. 2000

Biochemistry of Sports
Biochemical Foundations of Athletes' Endurance
Training Methods Promoting Endurance Development

The training Methods used to develop endurance have a selective impact on individual bioenergetic Functions. The most effective endurance training methods include continuous prolonged work (at either a uniform or variable pace), as well as repeat and interval training. These methods are typically classified according to whether they target the aerobic or anaerobic component of endurance.

Training aimed at developing the alactic anaerobic component of endurance most frequently employs repeat and interval work (interval sprinting). The primary objective of this training is to maximize the depletion of alactic anaerobic reserves in working Muscles and to enhance the stability of Key Enzymes of the alactic anaerobic system (Myosin ATPase and sarcoplasmic creatine phosphokinase) under conditions where anaerobic breakdown products accumulate (ADP, H₃PO₄, lactic acid, etc.). Achieving this goal is only possible through a high number of repetitions of short-duration, high-intensity exercises (lasting no more than 10–15 s at 90–95% W_max).

When using the repeat endurance training method with maximum power exercises, the rest intervals between efforts must ensure sufficiently complete restoration of the alactic anaerobic reserves expended during work—that is, they must correspond to the repayment time of the fast fraction of the O₂ debt and be at least 2.5–3 minutes. The general pattern of biochemical changes during such training loads is illustrated in Fig. 184.

The breakdown of high-energy phosphate compounds (ATP + PCr) during maximum power exercise leads to a sharp increase in The rate of O₂ consumption During the first few seconds post-exercise, driven by the oxidative resynthesis of PCr in the active muscles. The peak rate of this process corresponds to a delayed maximum in the O₂ consumption curve, observed during the 1st minute of recovery following exercise completion. During this period, the rate of non-metabolic excess CO₂ elimination decreases significantly. As shown in Fig. 183, the values for "peak" O₂ consumption and Blood lactate accumulation rise continuously up to the 5th–6th exercise repetition, indicating the gradual depletion of alactic anaerobic capacity. Once the critical threshold of PCr depletion in the working muscles is reached, maximum power immediately drops. This state is typically attained by the 8th–10th repetition, which can be considered optimal for this specific method of training the alactic endurance component.

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Fig. 184. Dynamics of Biochemical changes in athletes during repeated short-term exercises of maximum power

Unlike the repeat training method, where rest intervals are not strictly regulated, the interval method carefully selects rest durations to ensure the most pronounced effect on the targeted function. Varying this duration during repeated maximum power exercises directly influences the dynamics of biochemical shifts within the body (Fig. 185).

When rest intervals between exercises are reduced to 1 minute, a delayed O₂ consumption maximum is still observed, indicating the activation of processes that replenish alactic anaerobic reserves with each successive maximal effort. However, this maximum disappears when rest intervals are shortened to 30 seconds. Instead, a sawtooth curve emerges, featuring peak O₂ consumption rates at the end of each maximal effort and slight dips during the rest pauses. After the first 5–6 repetitions, the O₂ consumption rate stabilizes at a constant level corresponding to the severity of the interval work, which under these conditions depends on the chosen rest intervals. If rest intervals are reduced to 10 seconds, the peak O₂ consumption during exercise matches the maximal oxygen uptake (VO₂max). Shortening the rest intervals in this manner is accompanied by an enhanced excessive release of CO₂ during the first 5–6 repetitions, a rapid accumulation of lactic acid, and a drop in blood pH (Fig. 186). Significant acidification of the body's internal environment due to blood lactate accumulation (exceeding 10 mmol·L^-1) leads to a decline in the rate of the creatine phosphokinase reaction and maximum power output. A further increase in the number of repetitions alters the training effect of the interval work, shifting it toward a mixed aerobic-anaerobic character. Therefore, when utilizing short maximal efforts combined with brief rest intervals (under 30 s) in interval training, to achieve an alactic anaerobic training effect, the work should be performed in sets of 5–6 repetitions each, with rest intervals of at least 3 minutes between sets.

To develop the glycolytic anaerobic component of endurance, single maximal, repeat, and interval work methods can be employed. The chosen exercise parameters must ensure a maximal enhancement of anaerobic glycolytic transformations in the working muscles. Maximum efforts lasting between 30 seconds and 2.5 minutes meet these conditions. The dynamics of Biochemical changes in the body during such exercises are illustrated in Fig. 187.

Fig. 185. Influence of rest interval duration on The Nature of biochemical changes in athletes during interval sprint training: performing 10-second maximum power exercises with 10-second (a), 30-second (b), and 50-second (c) rest intervals

Repeatedly performing glycolytic anaerobic exercises with long, unregulated rest intervals allows the programmed training effect to be reproduced with each new repetition. The maximum number of exercise repetitions in this case depends on the depletion of Glycogen stores in the active muscles and the attainment of limiting acidification levels (typically by the 6th–8th repetition of the maximal effort).

During glycolytic anaerobic interval training, shortening the rest pauses does not alter the peak O₂ consumption level (which reaches its maximum in these exercises), but it leads to a rapid increase in recovery "excesses" of O₂ consumption, a higher rate of blood lactate accumulation, and pronounced fatigue. If the rest intervals relate to the work periods in a 1:1 or 1:1.5 ratio—meaning they are less than 1.5–2 minutes—the total number of exercise repetitions is reduced to 3–4 due to rapidly developing fatigue (see Fig. 187, a, b). At the same time, this achieves the highest rate of anaerobic Glycolysis in the working muscles and the highest blood lactate accumulation values.

To accomplish the necessary volume of work required to consolidate the training effect, interval work with short rest pauses is typically performed in sets of 3–4 repetitions, separated by 10–15 minutes of rest, which is necessary to restore work capacity following maximal anaerobic exertion.

Training aimed at developing the aerobic component of endurance utilizes methods of continuous single-bout exercise, repeat work, and several variations of interval work. To ensure a sufficient impact on aerobic METABOLISM when using continuous single-bout and repeat methods, the total duration of the exercise must be at least 3 minutes—sufficient for physiological adaptation (warm-up) and the attainment of a steady-state level of O₂ consumption. In continuous single-bout work, the load volume required to induce corresponding adaptive restructuring in the body is typically at least 30 minutes. An example of the body's biochemical response to this type of work is shown in Fig. 188.

Fig. 186. Changes in blood lactate levels and pH during interval sprint training

Fig. 187. Dynamics of biochemical changes in athletes during repeated maximal glycolytic anaerobic exercises: work-to-rest ratios of 1:1 (a), 1:2 (b), 1:4 (c), and 1:6 (d)

The intensity of continuous single-bout exercise must ensure significant activation of oxidative processes in the Tissues. Following the initial adaptation period, the O₂ consumption level stabilizes near its maximum values. Performing such work requires a substantial strain on the cardiorespiratory system, which is responsible for delivering O₂ to the working muscles. Throughout the exercise, pulmonary ventilation, Heart rate (HR), and blood pressure continuously increase.

The response of the autonomic support systems depends on the elevation of Anaerobic Metabolism indicators. Since the workload exceeds the anaerobic threshold, the release of "non-metabolic excess" CO₂ and the accumulation of blood lactate increase significantly as the exercise progresses. Qualified athletes are capable of sustaining this type of continuous work for 2.5–3 hours in the absence of pronounced shifts in anaerobic metabolism. A slight enhancement of anaerobic glycolysis in the working muscles is restricted to the initial stage, encompassing the first 5–6 repetitions of the exercise. Subsequently, blood lactate levels exhibit a downward trend.

Fig. 188. Dynamics of biochemical changes in athletes during prolonged continuous work

Fig. 189. Biochemical changes in athletes during repeated work with a mixed aerobic-anaerobic impact

Fig. 190 Biochemical changes in athletes during aerobic interval training

Short-segment interval training serves as an effective means of enhancing aerobic capacity. The BIOCHEMICAL FOUNDATIONS OF this interval training regime have already been examined when analyzing physiological responses to repeated short-term, maximal-power exercises with brief rest intervals.

Another option is a modified version of short-segment interval training known as Myoglobin interval training. This method involves very short work intervals (no more than 5–10 s) alternated with equally brief rest periods. The exercise intensity is quite high, yet submaximal (performed smoothly and without undue strain). During the brief work phases, intramuscular stores of myoglobin-bound O₂ are depleted, but they are rapidly replenished during the short rest pauses. This type of work can be performed in large volumes while maintaining a high rate of O₂ consumption, thereby contributing to The Development of aerobic efficiency.

A high level of endurance can only be achieved by simultaneously improving all its key components through a diverse range of means and methods that selectively target the relevant physiological functions and qualities of the athlete. The application of all these training tools must be grounded in an understanding of the fundamental patterns of biochemical adaptation during the training process.

Review Questions

1. What is meant by the term "endurance," and how is it manifested?

2. Which bioenergetic criteria can be used to assess the level of endurance development?

3. How does work output depend on the time limit of an exercise?

4. How does the metabolic state of the body change as exercise duration increases?

5. What is the metabolic relationship between the total amount of work performed to exhaustion and the time limit of the exercise?

6. Which training methods are used to develop individual components of endurance?

7. Which training methods are used to develop the alactic component of endurance?

8. Which training methods are used to develop the glycolytic aerobic component of endurance?

9. Which training methods are used to develop the aerobic component of endurance? What are the Biochemical characteristics of such work?

10. What is the core principle of myoglobin interval training?