**9. The hypotheses of physical nature: The role of the increase in temperature in muscular damage**

Numerous studies (Nielsen 1969; Nadel et al.,1972; Pahud et al., 1980) witness the fact of how the intramuscular temperature is higher during the negative work (i. e. eccentric contraction) in comparison to that seen in the course of positive work ( i.e. concentric contraction ) when the data is compared to a metabolic equivalent or to a ratio of heat production ( for further indepth analysis please see the specific box). In equivalent experimental conditions the eccentric contraction, in comparison to the concentric one, produces an increase in heat superior of about 1.2 degrees Celsius (Nadel et al., 1972), sufficient increase to determine a decrease of the viscosity of the sarcolemma equal to about 7% (Nagamoto et al., 1984). Such decrease in viscosity, although modest, would be able to activate the phospholipase A2, triggering in such a way an increase in the ratio of degradation of the cellular membrane (Chang et al., 1987). Other studies, carried out on muscle in vitro, would highlight as an increase of the temperature from 25 to 35 ° Celsius obtained by placing the muscle under a series of eccentric contractions, increases the risk of structural damage by a good 50% (Zerba et al., 1990) However, we must adopt care in interpreting the role of the increase of the muscle temperature in the field of its structural damage. Such care is obligatory above all considering the fact that, in the mentioned studies, the difference between the peak of temperature obtained during negative and positive work is essentially modest; secondly the absolute metabolic ratio would not seem, in this specific field, the most discriminating parameter. In addition to this, we must consider that the Fenn effect would theoretically foresee a ratio of minor heat during an eccentric contraction, in comparison to the theoretically predictable one in the course of an isometric and concentric contraction. In effect, the theoretic forecast carried out based on the Fenn effect, which would foresee a minor heat production during an eccentric contraction, would be confirmed also in some experimental data (Abbot and Aubert, 1951). All these observations could lead us to consider the highest production of heat observed in the course of negative work, not so much as an increase in the ratio of heat production on behalf of the muscle itself in similar conditions, but as the consequence of the drop of the ratio or heat removal by the muscle, which is registered during an eccentric contraction ( for further information please refer to the specific box.)

#### **9.1. Eccentric contraction and heat dispersion**

**ii.** From the time that a progressive increase of the number of eccentric contractions, it

From a practical but above all rehabilitative /preventive point of view, this data underlines the

**i.** Increasing the muscle capacity in the field of specific stamina regarding the eccentric

**ii.** Increasing the maximum value of eccentric force, limiting the decrease of the latter

Numerous studies (Nielsen 1969; Nadel et al.,1972; Pahud et al., 1980) witness the fact of how the intramuscular temperature is higher during the negative work (i. e. eccentric contraction) in comparison to that seen in the course of positive work ( i.e. concentric contraction ) when the data is compared to a metabolic equivalent or to a ratio of heat production ( for further indepth analysis please see the specific box). In equivalent experimental conditions the eccentric contraction, in comparison to the concentric one, produces an increase in heat superior of about 1.2 degrees Celsius (Nadel et al., 1972), sufficient increase to determine a decrease of the viscosity of the sarcolemma equal to about 7% (Nagamoto et al., 1984). Such decrease in viscosity, although modest, would be able to activate the phospholipase A2, triggering in such a way an increase in the ratio of degradation of the cellular membrane (Chang et al., 1987). Other studies, carried out on muscle in vitro, would highlight as an increase of the temperature from 25 to 35 ° Celsius obtained by placing the muscle under a series of eccentric contractions, increases the risk of structural damage by a good 50% (Zerba et al., 1990) However, we must adopt care in interpreting the role of the increase of the muscle temperature in the field of its structural damage. Such care is obligatory above all considering the fact that, in the mentioned studies, the difference between the peak of temperature obtained during negative and positive work is essentially modest; secondly the absolute metabolic ratio would not seem, in this specific field, the most discriminating parameter. In addition to this, we must consider that

number of cycles leading to structural weakness", up and to the right,

**9. The hypotheses of physical nature: The role of the increase in**

contraction, in such a way to increase the quantity of eccentric work supported by the same muscle, moving the curve of structural weakness of the relation "stress-

in conjunction with the increase of the number of cycles. To this end it is important to remember how the value of stamina- in this case of stamina in eccentric regimedepends on the values of maximum force- and so in this specific case of maximum

the risk of injury.

eccentric force.

**temperature in muscular damage**

importance of:

18 Muscle Injuries in Sport Medicine

would lead to a contextual progressive decrease of the peak of maximum eccentric force, due to the fatigue phenomena, expressed by the muscle, there would exist a limit of the value of eccentric force, below which the muscle would be exposed to the risks of structural damage. According to McCully and Faulkner, such a limit would be between 60 and 80% of the maximum value of eccentric force. In other words when the decrease of the production of eccentric force drops below 20-40% the muscle runs

> The production of metabolic heat and its disposal, may be modeled through a central "heat producer" nucleus, made up of skeletal muscles, bowels, internal organs and the central nervous system, a "means of transport", made up of the circulatory system and of a "cooling surface", made of skin. During an eccentric contraction we can see a transient and intermittent mechanism of vasoconstriction which strongly limits the capacity of transporting heat, produced by the muscular contraction, on the part of the circulatory system. For this reason the highest production of heat during negative work, in comparison to the production of heat during positive work, it is essentially attributable to the reduced ratio of degradation of heat which occurs during negative work, caused by the aforementioned vasoconstriction mecha‐ nism.
