Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

There's no slowing stocks today on the latest information bites out of Washington. The Dow Jones Industrial Average (^DJI 0.67%) exploded out of the starting gate this morning and hasn't looked back. The blue-chip index has soared more than 230 points, or a whopping 1.6%, as of 2:45 p.m. EDT. While the debt ceiling debate isn't something that should alter your investing strategy, a few big-name stocks are making waves today, led by UnitedHealth's (UNH -1.98%) solid gains. Let's catch up on what you need to know.

UnitedHealth hits the gas
UnitedHealth's stock has jumped 3% today to lead the Dow higher. There's little news out of the company, which is understandably in a period of change as Obamacare is rolled out across the country. While health care reform's been a sticky subject so far, UnitedHealth hasn't suffered for it: The stock's one of the best-performing Dow members year to date, with shares jumping more than 33% so far in 2013.

Much of UnitedHealth's success is due to the company's ability to expand its industry-leading membership base. The company is America's largest public insurer, and UnitedHealth hasn't let off the gas pedal in 2013. UnitedHealth counted 45 million total medical subscribers at the end of June, a 25% year-over-year gain. That's outstanding growth for an organization of this size and will help it hedge against any unwanted side effects of health-care reform, such as higher costs in state exchanges -- a factor that helped push UnitedHealth to opt out of participating in numerous individual insurance exchanges in states including California.

However, investors shouldn't expect such rapid growth every year. Part of the big gains in 2013 come from the integration of the U.S. military's TRICARE insurance system into UnitedHealth's portfolio, a move that added nearly 3 million subscribers. The company also made some smart moves abroad that should help growth in the future, with its purchase of Brazilian insurer Amil last year standing out. With the insurance industry in flux as Obamacare launches, UnitedHealth is one of the safest and strongest stocks in the industry.

Big Oil's not having such a good day today, however. As the Dow rises, ExxonMobil (XOM 0.57%) and Chevron (CVX 1.20%) are among the worst performers on the index, with the former gaining just 0.2% while the latter has lost 0.5%. Chevron announced today that third-quarter earnings would fall significantly below its second-quarter results due to lower fuel margins in its refining business. The company also said in its interim quarterly update that U.S. net oil-equivalent production is down from the second quarter.

Exxon's been taking a blow from low natural-gas prices, a factor that crippled the company's second-quarter earnings. However, Exxon also sees natural-gas demand skyrocketing in coming years -- and the sheer economies of scale could be enough to help outweigh recessed margins and please investors. In the long run, Exxon and Chevron remain two of the biggest giants in the energy sector and two of the best-placed businesses to capitalize on America's resurgent energy boom.