Recent findings suggest that both the lack of physical activity and prolonged periods of sedentary behavior significantly increase the risk of chronic diseases. A growing concern is that they function independently of each other. Therefore, individuals meeting minimum guidelines for movement but working in environments where movement is limited throughout the day are also at risk. There seems to be a relevant relationship between the time spent seated and the risk for morbidity. Interestingly, even exercising three times a week at a moderate intensity, utilizing fitness equipment appears to be inadequate to offset an otherwise sedentary lifestyle. One investigation sought to examine the response of select musculature to long periods of sedentarism. The authors analyzed quadriceps and hamstring muscle inactivity as well as activity during normal daily life. Eighty-four volunteers (44 females, 40 males, 44.1 ±17.3 years, 172.3 ±6.1 cm, 70.1 ±10.2 kg) were measured during normal daily activities using shorts that measured muscle electromyographic (EMG) activity (recording time 11.3 ±2.0 hours). EMG data was normalized to isometric MVC (EMG(MVC)) during knee flexion and extension, and inactivity threshold of each muscle group was defined as 90% of EMG activity during standing (2.5 ±1.7% of EMG(MVC)). During normal daily life, the average EMG amplitude was 4.0 ±2.6% and average activity burst amplitude was 5.8 ±3.4% of EMG(MVC); this average being below the EMG level required for walking (5 km/h corresponding to EMG level of about 10% of EMG(MVC)). Using the proposed individual inactivity threshold, thigh muscles were inactive 67.5 ±11.9% of the total recording time and the longest inactivity periods lasted for 13.9 ±7.3 min (2.5-38.3 min). Women had more activity bursts and spent more time at intensities above 40% EMG(MVC) than men.
In conclusion, during normal daily life, the locomotor muscles are inactive about 7.5 hours, and only a small fraction of the musculature’s maximal voluntary activation capacity is used. Some daily non-exercise activities such as stair climbing produce much higher muscle activity levels than brisk walking, and replacing sitting with standing can considerably increase cumulative daily muscle activity. Trainers need to influence clients to not only train 2-3 times per week, but additionally participate in regular daily movement. Taking the stairs, walking the dog, and simply moving more will certainly contribute to reduce health risk associated with sedentarism.