Responses of muscle mass, strength and gene transcripts to long-term heat stress in healthy human subjects

Intramuscular heating through fluidotherapy and heat shock protein response

CONTEXT

Therapeutic modalities that can increase intramuscular temperature commonly are used to treat injuries in the clinical setting. Researchers recently have suggested that the physiologic changes occurring during an increase in temperature also could provide a cytoprotective effect for exercise-induced muscle damage.

OBJECTIVE(S)

To determine if the Fluidotherapy treatment increases the inducible expression of heat shock protein (HSP), to identify the rate of heating that occurs in the lower extremity with Fluidotherapy treatment, and to evaluate the relationship between the inducible expression of HSP and temperature.

DESIGN

Controlled laboratory study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Six male (age = 21.67 ± 1.63 years, height = 180.09 ± 4.83 cm, mass = 87.60 ± 10.51 kg) and 6 female (age = 24.60 ± 4.59 years, height = 151.05 ± 35.76 cm, mass = 55.59 ± 14.58 kg) college-aged students.

INTERVENTION(S)

One lower extremity was randomly selected to receive the heat treatment, and the other extremity received no treatment.

MAIN OUTCOME MEASURE(S)

We measured intramuscular temperature every 10 minutes, determining peak intramuscular temperature by 2 identical sequential measurements, and we analyzed the time to peak temperature. We analyzed the amount of HSP70 expression and HSP27P:T (ratio of HSP27 to the total HSP27 expression) in the gastrocnemius and soleus muscles and measured baseline skinfold thickness and estradiol levels.

RESULTS

Fluidotherapy increased intramuscular temperature by 5.66 ± 0.78°C (t11 = 25.67, P < .001) compared with baseline temperature, with a peak temperature of 39.08°C ± 0.39°C occurring at 84.17 ± 6.69 minutes. We did not find a heat treatment effect for HSP70 or HSP27P:T in the gastrocnemius or soleus muscles (P > .05). Peak temperature and the percentage change of HSP70 were positively correlated for the gastrocnemius and soleus muscles (P < .05). We found no other correlations for skinfold thickness, sex, or estradiol levels (P > .05). No effect of sex for skinfold thickness or estradiol levels at baseline was discovered (P > .05).

CONCLUSIONS

This Fluidotherapy protocol increased the intramuscular temperature to a therapeutic level; however, it did not stimulate inducible HSP70 or HSP27P:T in the soleus and gastrocnemius muscles regardless of sex or skinfold thickness. These data confirmed that Fluidotherapy is an effective heating modality but suggested it is not an effective method for stimulating an HSP response in the lower limb.

Absence of heat shock transcription factor 1 retards the regrowth of atrophied soleus muscle in mice

Effects of heat shock transcription factor 1 (HSF1) gene on the regrowth of atrophied mouse soleus muscles were studied. Both HSF1-null and wild-type mice were subjected to continuous hindlimb suspension for 2 wk followed by 4 wk of ambulation recovery. There was no difference in the magnitude of suspension-related decrease of muscle weight, protein content, and the cross-sectional area of muscle fibers between both types of mice. However, the regrowth of atrophied soleus muscle in HSF1-null mice was slower compared with that in wild-type mice. Lower baseline expression level of HSP25, HSC70, and HSP72 were noted in soleus muscle of HSF1-null mice. Unloading-associated downregulation and reloading-associated upregulation of HSP25 and HSP72 mRNA were observed not only in wild-type mice but also in HSF1-null mice. Reloading-associated upregulation of HSP72 and HSP25 during the regrowth of atrophied muscle was observed in wild-type mice. Minor and delayed upregulation of HSP72 at mRNA and protein levels was also seen in HSF1-null mice. Significant upregulations of HSF2 and HSF4 were observed immediately after the suspension in HSF1-null mice, but not in wild-type mice. Therefore, HSP72 expression in soleus muscle might be regulated by the posttranscriptional level, but not by the stress response. Evidence from this study suggested that the upregulation of HSPs induced by HSF1-associated stress response might play, in part, important roles in the mechanical loading (stress)-associated regrowth of skeletal muscle.