Walk It Off! the Influence of Physical Activity Level on the Recovery from Damaging Resistance Exercise

After completing novel activity or exercise we may experience exercise-induced muscle damage (EIMD), resulting in a period of reduced muscle function and delayed onset muscle soreness (DOMS). DOMS is characterized by muscle pain and tenderness that typically resolves within a week. While the precise cause of DOMS is unknown, there is growing evidence implicating damage to the connective tissue that surrounds our muscle fibers and is related to a small amount of inflammation. This inflammation is a normal part of our body's ability to recovery from injuries and may be visualized through the use of ultrasound technology. A variety of recovery techniques have been proposed that may help with the recovery of DOMS such as massage and electrical muscle stimulation, but these are not always accessible. Therefore, we are interested in investigating whether the number of daily steps can affect how you experience DOMS.

Skeletal muscle pain and tenderness typically follow an unaccustomed bout of physical activity involving eccentric or lengthening contractions. The intensity of pain peaks between 24 and 72 h following the cessation of activity and subsides completely between 5 and 7 days after exercise. Delayed-onset muscle soreness (DOMS) refers to physical discomfort, while associated impairments to muscle strength and function reflect the occurrence of exercise-induced muscle damage (EIMD). The result is reduced performance and increased likelihood of further injury during the affected period. In beginners, DOMS may also reduce the likelihood of continuing exercise.

Despite its ubiquity in sport and exercise, the precise mechanism of DOMS remains uncertain. Potential mechanisms include EIMD, inflammation, and immune cell infiltration among others. More recently, evidence has emerged suggesting a greater role of intramuscular connective tissue damage in causing DOMS. Following an acute bout of eccentric exercise, the fascial connective tissue exhibits greater swelling than after a concentric exercise. Furthermore, this swelling was correlated with the severity of DOMS. This novel evidence may aid in directing strategies to mitigate the duration and severity of DOMS.

A variety of treatments for DOMS have been explored with varying degrees of efficacy. Massage has been shown to effectively mitigate DOMS following exercise as it passively increases muscle blood flow and reduces muscle oedema. Electrostimulation has also been shown to produce analgesic effects following unaccustomed exercise, although results are inconsistent. Differences in the treatment design may produce discrepant findings with longer duration, lower frequency stimulation alleviating DOMS, in contrast to shorter duration, higher frequency stimulation. Furthermore, lower-intensity longer-duration recovery modalities that promote muscle blood flow may partially ameliorate the ergolytic effects of DOMS. Based on these findings, active recovery consisting of low-intensity exercise following training which facilitates muscle blood flow might be expected to improve recovery from DOMS. However, active recovery strategies such as submaximal cycling or jogging following exercise has little effect on recovery from unaccustomed exercise. While these protocols do promote the muscle blood flow in the days following the bout of exercise, their intensity may be too great to allow for recovery of the muscle while their duration may be too low to produce a sustained effect. It has recently been shown that low daily step counts (\<5000/day) can interfere with the normal recovery from aerobic exercise and reduce the normal benefits to metabolism, highlighting that our habitual activity levels might be the most important variable in recovering from and adapting to the stress of exercise. Therefore, the purpose of this study is to investigate the effect of high (\>10,000 steps) and moderate (\<5,000) daily step counts on recovery from an unaccustomed bout of resistance exercise.

Eligibility Criteria:
Inclusion Criteria:

- Healthy, recreationally active male and female participants (i.e., weekly MET-minutes \> 3000 assessed by International Physical Activity Questionnaire).

Not having a health condition that would compromise their ability to safely participate in the strenuous physical activity involved in our study screened for by the get active questionnaire.

Between 18 and 35 years old.

Body mass index (BMI) between 18.5-30

Self-reported not having engaged in resistance exercise and/or lower body plyometrics for at least 3 months prior to the study.

Willing to abide by the compliance rules of this study.

Self-reported regular menstrual cycle (25-35d) within the last 3 months (female participants).

Exclusion Criteria:

Inability to adhere to any of the compliance rules judged by the principal investigator or medical doctor.

Self-reported regular tobacco use.

Regular use of non-steroidal anti-inflammatory drugs (e.g., Advil)

Use of oral contraceptives (female participants).